Two New York boys reported missing last week have been found dead in different rivers in Manhattan, police say.

Alfa Barrie, 11, and Garrett Warren, 13, who authorities believe were friends, were last seen together in Harlem sometime between May 12 and May 13, police said during a news conference Tuesday.

The New York Police Department's Harbor Unit found the bodies of the boys several days apart. They were found more than two miles away from one another in two separate rivers, an NYPD spokesperson told CNN.

Garrett was found on Thursday in the Harlem River near the Madison Avenue Bridge, which connects Manhattan and the Bronx. Two days later, police found Alfa's body in the Hudson River near the Upper West Side, according to the NYPD spokesperson.

Surveillance video last showed the boys leaving a home together and traveling past a large group of people, Deputy Chief Brian Gill said at Tuesday's news conference.

Alfa was reported missing in the early morning of May 14, and Garrett was reported missing in the afternoon of May 15, police say.

Authorities say the boys attended separate schools but were believed to be friends, with police connecting the two cases after Garrett was reported missing.

The NYPD said the investigations into the boys' deaths remains ongoing. The New York City medical examiner is investigating a cause of death for both boys, an NYPD spokesperson said.

CNN affiliate ABC 7 reported family and friends gathered at a mosque in the Bronx after Alfa's body was found.

Family friend Adhmadou Diallo said the boy was close with his mother and helped out at home.

"Every time he gives his mommy a goodbye kiss when going to school -- and that's what happened on Friday when he left," Diallo told the outlet.

ABC 7 reported Alfa was a sixth-grade student at Democracy Prep Public School in Harlem, which released a statement mourning the loss of the "funny, bright, witty, inquisitive, and brave child."

"He will be sorely missed by his teachers and fellow students," the school said. "We also stand in solidarity with the family of Alfa's friend, Garrett Warren. While he was not a student, we understand that this is a difficult time for his community as well and share our prayers with them."