Two people were killed and at least seven were injured — some seriously — in an early-morning Camden apartment building fire Sunday that sent residents jumping from third-story windows to escape the flames.

One firefighter sustained a shoulder injury in the three-alarm blaze that broke out about 3 a.m. on the 3400 block of Cramer Street, officials said.

Authorities said late Sunday that the fire had been intentionally set and announced the arrest of Brandon Adams, 34, whom they described as homeless. He was charged with two counts of first-degree murder, the Camden County Prosecutor’s Office said late Sunday night.

Authorities did not provide more information about the two men who were killed. At least nine other people were taken to hospitals for treatment, and about three dozen people were displaced, according to the prosecutor’s office.

Investigators from the Fire Marshal’s Office and the prosecutor’s office were on the scene Sunday morning.

“It’s a full-fledged investigation,” Camden Mayor Frank Moran said. “They want to get to the bottom of what was the cause of the fire.”

Displaced residents of the 22-unit apartment building are receiving assistance from the Red Cross and the city’s Department of Human Services at nearby Davis Elementary School. They are expected to be housed in motels temporarily if they have no other options.

“We haven’t had a fire like this in a while,” Moran said.

Betsy Rivera said her son-in-law, who lives in the apartment building with Rivera’s daughter and two grandchildren, had tried to help people get out of the building using a ladder.

“For some, it was too late,” Rivera said. “They jumped out of the building.”

Rivera’s daughter, who asked not to be identified, said she didn’t have time to grab any of her family’s personal belongings before fleeing the building. She said the hallway was filled with smoke when she opened her door. The only thing she took was the baby bag for her 6-month-old son.

“I didn’t have a chance to get anything,” she said. “I just had to grab my kids and go.”

Moran said that the apartment building did not have any major code violations and that the fire alarm was working properly.

While firefighters were on the scene of the Cramer Street fire, they also got a call for a second fire nearby, leaving them stretched thin.

“I thank our firefighters for acting swiftly and doing an amazing job, as they always do,” Moran said.