Thousands of ethnic minority Muslims surrounded a mosque in southwestern China over the weekend in a last-ditch effort to prevent what they said was an attempt by authorities to remove its dome and minarets, as a crackdown on religious freedoms widens.

The apparent alteration of a mosque belonging to the Hui ethnic group in Najiaying village, Yunnan province comes amid a sweeping campaign unleashed by China's leader Xi Jinping to "sinicize" religion.

The policy aims to purge religious faiths of foreign influence and align them more closely with traditional Chinese culture -- and the authoritarian rule of the officially atheist Communist Party.

In recent years, authorities have removed overtly Islamic architecture -- destroying domes and tearing down minarets -- from more than a thousand Hui mosques across the country, Hui activists say, with the Najiaying mosque being one of the last holdouts.

Now, the "sinicization" campaign is finally coming for Najiaying -- a historic home to the Hui and an important hub for Islamic culture in Yunnan, an ethnically diverse province on China's borders with Southeast Asia.

But the push has faced a fierce backlash from local residents.

Videos posted on social media and geolocated by CNN show residents clashing with lines of police officers in riot gear, who blocked off the entrance to the mosque and pushed back the crowd with shields and batons.

Residents shouted back in anger, with some hurling water bottles and bricks at the police, the videos show.

"This is our last bit of dignity," a local witness told CNN. "It's like coming to our house to demolish our home. We can't allow that to happen."

The source, who declined to be named over fears for personal safety, said thousands of Hui residents -- including men and women, elderly and children -- had gathered around the mosque on Saturday, under the close watch of more than 1,000 police officers deployed nearby.

"After arriving at the mosque, we realized that they had driven the cranes into the compound and were ready for the forced demolition," the source said, adding that scaffolding had already been erected around the mosque.

Tensions escalated around 1 p.m., with worshipers demanding to enter the mosque for noon prayers, the source said. They said they saw police officers hitting the crowd with batons, which prompted some residents to clash with police.

Dozens of protesters were arrested by police at the scene, the source said. Ma Ju, a prominent Hui activist who now lives in the United States and has kept close contact with Najiaying residents, said about 30 people were arrested.

CNN cannot independently verify the claims and has reached out to the local police and government for comment. CNN has also reached out to the Yunnan provincial government and its bureau for religious affairs for comment.

'Our nightmare is only starting now'

The hours-long standoff on Saturday yielded a temporary win for the protesters, who streamed into the mosque as the police retreated, according to the witness and online videos.

Throughout Saturday night and Sunday, residents took turns to guard the mosque, fearing that authorities would return to demolish its large centerpiece green dome and four minarets, the source said.

But repercussions quickly followed, according to those CNN spoke with.

By Sunday afternoon, word started to spread that authorities were arresting more people, according to the source.

On Sunday evening, law enforcement authorities in Nagu township, where Najiaying is located, issued a stern but vague statement. Without mentioning the protest or the mosque, it said police were investigating an incident that took place on Saturday, which "seriously disrupted social order" and caused "vile social impact."

The authorities also called on the "organizers and participants" of the incident to turn themselves in before June 6 to receive leniency, and encouraged the public to report on each other.

By Monday, Najiaying was shrouded in a blanket of fear, the source said.

The internet has been cut off in many neighborhoods. Drones buzzed overhead and surveilled the village. Public loudspeakers blasted the authorities' message on repeat, urging protesters to turn themselves in, according to the source and Ma, the US-based activist.

"It feels like our nightmare is only starting now," the source told CNN. "Everyone is in fear...We don't know what's going to happen next."

Other local residents appeared fearful to speak out.

One shop owner reached by CNN on the phone said: "You journalists should come here to report on what's happening to us." When asked by CNN to explain what happened, he replied he "didn't know" and hung up.

'This is what they did to Xinjiang'

This is not the first time that Hui Muslims have engaged in a tense standoff with authorities to protect a mosque.

In 2018, thousands of Hui residents in Ningxia, in the country's northwest, staged a sit-in protest for three days to prevent authorities from demolishing a newly constructed mosque.

The local government held off on the demolition, but later replaced the mosque's domes and minarets with traditional Chinese-style pagodas.

The architectural overhaul of mosques has come with allegations of shrinking religious freedoms for the Hui, a 11 million-strong ethnic minority that live in scattered pockets throughout China from the northwest to the coastal cities in the east, including an officially designated "autonomous region," Ningxia.

Believed to be distant descendants of Arab and Persian traders, the Hui have been well assimilated into broader Chinese society dominated by the ethnic Han majority.

Most speak Mandarin, live alongside the Han, and in recent decades had been given more space to practice their faith than other ethnic groups.

But Hui activists say their ethnic group has become the latest target in the Communist Party's crackdown on Islam, which began in the western region of Xinjiang.

Since at least 2017, the Chinese government has been accused of detaining more than a million Uyghurs and other Muslim minorities in internment camps in Xinjiang and conducting forceful assimilation to suppress their cultural and religious identity.

A United Nations report last year accused the Chinese government of serious human rights violations against Uyghurs that may amount to "crime against humanity."

China has repeatedly denied these accusations and insisted that the massive camps are voluntary "vocational training centers."

'Not just domes'

Hui activists and rights groups claim authorities have stepped up efforts in recent years to restrict religious practices of Hui Muslims across China, including the shuttering of Islamic schools, Arabic classes and barring children from learning and practicing Islam.

The implementation of the "sinicization" campaign has "had the effect of expunging communities of their connections to Hui culture, religion, and each other so thoroughly that some leaders view the erasure of a meaningful Hui identity within another generation as being a likely possibility," according to a report submitted to a UN treaty body in January by the Chinese Human Rights Defenders and the Hope Umbrella International Foundation.

Ma, the US-based Hui activist who founded the Hope Umbrella International foundation, said Hui in China are now living in a constant state of fear.

Over two hundred mosques in Yunnan have already lost their domes and minarets, according to Ma, adding to the more than a thousand mosques in the country's northwest.

CNN is unable to independently verify the number of mosques affected, and has reached out to the Chinese government for comment on the accusations made by Hui activists.

"At first, people thought it was only a question of architectural style...but it soon became apparent that (the government) is not only removing the domes from the mosques, but also removing their religious and social functionality," Ma said.

Under a raft of restrictions imposed by the government, many Hui are now afraid to go to the mosque, which has long been a center of religious and social life for their communities, Ma said.

The end goal of the party is to implement a policy of "cultural and religious genocide," just as it did in Xinjiang, he said. The Chinese government has denied accusations of genocide.

For the resident in Najiaying, the government's plan to change the design of the mosque is only the harbinger of a harsher crackdown to come.

"This is only the first step. What we worry about is after that, (the authorities) will ban our children from going to (religious) classes, bar minors from entering mosques and forbid us from studying the Quran," they said, referring to the alleged restrictions that have been imposed on Hui communities across China.

"After they trampled on your dignity, they will suppress you step by step, and assimilate the Hui ethnic group completely into the Han, generation by generation. Because we know, this is what they did to Xinjiang," they said.

Despite the permeating culture of fear, he has vowed to "fight till the end" for the freedom of belief and the dignity of the Hui ethnicity.

"We commoners don't ask for much. We just want to have our own religious freedom. We just want to live in peace," they said.

"I want the world to know what we're going through right now, and what we're fearing next."