A power outage overnight at a Los Angeles hospital prompted the evacuation of more than 200 patients from a building housing neonatal intensive care and OBGYN units, according to the Los Angeles Fire Department.

The outage occurred in a six-story building at White Memorial Hospital, LA City Fire Capt. Cody Weireter told reporters Tuesday morning, calling it a "very large scope emergency."

Of the 271 patients at the facility, 21 were deemed critical, Weireter said.

It's unclear if the outage was caused by or related to Hilary, which struck Southern California on Sunday as a tropical storm with heavy rain and flooding before weakening to a post-tropical cyclone.

At White Memorial Hospital, "LAFD firefighters and paramedics had to work in a coordinated effort to transport (patients) down the stairs and the stairwells to awaiting ambulances," Weireter said. Those ambulances will transport the critical patients to nearby hospitals, while firefighters take the remaining, non-critical patients to another facility on the hospital's campus.

"At this point we are moving as quickly as possible to try and get these patients transported," Weireter said.

CNN has reached out to the hospital for additional information.

The fire department initially received a call at 11:45 p.m. local time Monday that the building had lost power and its backup generators were not working, the department previously told CNN. Officials responded to assist in the evacuation, with priority given to patients with urgent needs, such as those on ventilators.