The death toll from the partial collapse of a residential building in Miami rose to four on Friday morning with dozens still unaccounted for, as rescue workers raced to clear debris and search for survivors.

US president Joe Biden declared an emergency in the state of Florida after the apartment building collapsed suddenly early on Thursday with residents inside. Fears are rising that the death toll at the site, just north of Miami Beach, could continue to climb as the search proceeds.

Dozens of people have been pulled out of the rubble, with 120 found so far but 159 unaccounted for.

“I woke up to learn that three bodies had been pulled from the rubble last night,” bringing the death toll to four, Daniella Levine Cava, the mayor of Miami-Dade county, told ABC’s Good Morning America on Friday. “Devastating news for families waiting for any hope of survival. We will continue to search.”

She said firefighters had been working through the night “from above and below”, and that she was “very hopeful” there were still survivors in the rubble.

Biden ordered federal assistance to supplement state and local response efforts. The emergency action authorises the Department of Homeland Security’s Federal Emergency Management Agency to co-ordinate “all disaster relief efforts”, a White House statement said on Friday.

“Whatever help you want the federal government to provide, we’re waiting, just ask us, we’ll be there, we’ll be there,” said Biden.

Ron DeSantis, Florida governor, late on Thursday declared a state of emergency in Miami-Dade county, which cleared the way for FEMA to come to the site and provide assistance to rescue crews and affected families.

Rescue authorities arrived in the beachfront town of Surfside to find that the north-east section of the 12-storey Champlain Towers South had collapsed.

Ray Jadallah, chief of operations at Miami-Dade Fire Rescue, described the efforts as slow and dangerous and said that sonar, cameras and rescue dogs were being used to search for anyone trapped beneath the rubble.

“We did receive sounds. Not necessarily people talking, but sounds; what sounds like people banging,” Jadallah said at a news briefing on Thursday. “Short of that, we haven’t heard any voices coming from the pile.”

Officials said it was too soon to know what caused the collapse of the tower, which was built in the early 1980s. Alfredo Ramirez, director of the Miami-Dade county police department, said his detectives, as well as state and federal authorities, would commence an investigation into possible causes once the search and rescue operations were completed.

“I was woken by what sounded like thunder,” resident Barry Cohen told the BBC. “It looked like a bomb had exploded: dirt and dust and smoke all over the place. The whole building just shook with a huge explosion.”