Two construction workers are dead and five injured after part of a construction crane collapsed at a building site in Miami Tuesday.

Witnesses said a metal boom fell from the top of a 30-storey condominium project and crashed into a house that the contractor was using as an office.

Three construction workers were taken to hospital in critical condition, said Miami Fire Department spokesman Lt. Ignatius Carroll. He said one worker died immediately and another succumbed to his injuries in hospital.

Carroll said the wreckage of the crane was still a danger to workers.

"One thing that's working against us is that the crane is still somewhat unstable," he said. "And we're trying to make sure that it's stable while we are working down there."

Part of the unoccupied home that was being used as an office on the construction site was wrecked by pieces of the falling crane.

It was the second collapse of a large construction crane in an American city in just under two weeks.

On March 15, a crane toppled in New York City's East Side, killing seven people and injuring 10. Investigators say two metal collars that bound sections of the seven-and-a-half-storey crane together burst and left the crane without any support.

It first fell onto the building that was under construction before collapsing onto a neighbouring townhouse. The owner of the townhouse remains in a critical condition and a woman who was staying with him was among the dead.

A New York City building inspector, Edward Marquette, was arrested last week and charged with falsifying business records. New York's police commissioner said Marquette had lied about inspecting the crane.

Relatives of one of the construction workers killed in the incident have launched a $30 million lawsuit against the city, alleging negligence.

With files from the Associated Press