Rescue crews on the scene of a deadly beachfront apartment tower collapse in Miami say they have heard banging and other noises from beneath the mounds of rubble.

At least two Australians, and possibly several more, are feared among nearly 100 people still missing after the Champlain Towers South condominium collapsed to the ground in Surfside, a barrier island town across Biscayne Bay from Miami, early on Thursday (local time).

The Department of Foreign Affairs and Trade said on Friday it was aware of reports Australians might have been caught up in the disaster.

“The Australian embassy in Washington is closely monitoring developments and making urgent enquiries to determine if any Australians were affected,” it said.

Miami resident Joseph Waksm, who is originally from Australia, said earlier he had not been able to contact an Australian couple who were thought to have been inside the 11-storey Surfside apartment building.

“We have friends who live in that building from Australia and they are unable to be communicated with,” Mr Waks said.

“We are hoping for the best. Only good news.

“They both became grandparents yet again a few hours before the tragedy.

“We still cannot believe it.”

Mr Waks said the couple, aged in their 70s or 80s, were originally from Sydney but had also lived in Melbourne.

In addition, local journalist Danny Rivero, wrote on Twitter: “We’ve been told many Argentinians and Australians were in the building as well, and that all are unaccounted for. This is an international disaster.”

At least one person has been confirmed dead after the tower collapse, but Miami-Dade County Mayor Daniella Levine Cava said 99 people remained unaccounted for some 18 hours after the collapse – although some might not have been in the building at the time. More than 30 people had been rescued.

Fire Rescue Assistant Chief Ray Jadallah said some of the dozens of rescuers scouring the area had heard sounds from under the rubble.

“Not necessarily people talking, but sounds. What sounds like people banging, not people but sounds of a possibility of a banging. We haven’t heard any voices coming from the pile,” he said.

Miami-Dade Fire Rescue officials said more than 80 units responded to the collapsed building. It involved 55 apartment units.

What caused the 40-year-old high-rise to tumble into a heap in a matter of seconds was not immediately known, though local officials said the 12-storey tower was undergoing roof construction and other repairs.

Surfside mayor Charles Burkett said the building collapse was “less likely than a lightning strike.”

“It looks like a bomb went off but we are pretty sure a bomb didn’t go off,” he said. “You just don’t see buildings like this fall down in America.”

Footage from WPLG Local 10, a Miami TV station, showed a rescue team pulling a boy from piles of debris and rebar, and firefighters using ladder trucks to rescue residents trapped on balconies.

The search effort was slowed by at least one fire that burned at the site as emergency crews doused the rubble with water, local media reported.

Footage captured by a security camera nearby showed an entire side of the building crumbling in two sections, one after the other, in billowing clouds of dust about 1.30am.

The Champlain Towers South had more than 130 units, about 80 of which were occupied. It had been subject to various inspections recently due to the recertification process and the adjacent building construction.

Florida Governor Ron DeSantis, who toured the scene on Thursday afternoon, later signed an executive order declaring a state of emergency for Miami-Dade County to hasten access to federal disaster assistance.

Among the missing are 22 South Americans – nine from Argentina, six from Paraguay, four from Venezuela and three from Uruguay, according to officials in those countries.

Among the Paraguayans are Sophia López Moreira, the sister of first lady Silvana Abdo, her husband Luis Pettengill, her three children and the family’s assistant, the country’s authorities said.

Mr Burkett said building manager had told him the tower was quite full when it collapsed, and the death toll was likely to rise.

“The building is literally pancaked,” he said.

-with AAP