MIAMI: A 12-story oceanfront apartment block in Florida partially collapsed early Thursday, killing at least one person and leaving dozens unaccounted for as rescuers combed the rubble for possible victims.

Video footage posted online showed a large portion of the building in the town of Surfside - just north of Miami Beach - reduced to rubble, with the apartments' interiors exposed.

It was unclear what caused the building to collapse, nor how many people were inside at the time, since it was occupied by a mix of full-time and seasonal residents and renters according to Miami-Dade County Commissioner Sally Heyman.

"It's hard to get a count on it," Heyman told CNN. "It is 51 people who were supposedly, supposedly, residing there at the time (and) have not either called out or had people call in to reach them."

"But you don't know between vacations or anything else. So we're still waiting. And unfortunately, the hope is still there, but it's waning," she told CNN.

Around 55 apartments were affected by the collapse, according to Miami-Dade Fire Rescue Assistant Chief Ray Jadallah who told a news conference that emergency services arrived at the scene at around 1:30 am, evacuating 35 people from the building. Some residents were able to walk down the stairs to safety while others had to be rescued from their balconies.

One death was confirmed by Surfside mayor Charles Burkett, and Heyman said some 14 survivors had been recovered from the rubble.

At least 18 Latin American nationals are missing after an oceanfront apartment block near Miami Beach partially collapsed on Thursday, according to consular officials.

Three Uruguayans, six Paraguayans and nine Argentines have been reported missing following the pre-dawn collapse, according to the country's consulates in Miami.