HORRIBLE ACCIDENT: The crane collapse killed at least four people. -- PHOTO: AP

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At least four people were killed and a dozen others injured in what was described as one of the worst accidents the city has ever suffered.

The white crane, reaching 19-storeys high when it collapsed, fell during construction of a 43-storey building on 51st Street, splitting into pieces shortly after 2pm.

The collapse occurred while the crane was being jacked up to reach the required height.

'I saw the crane crashing, splitting in half,' said witness Greta Welkhammer.

It pulverised a four-storey townhouse and demolished parts of five other buildings.

Ms Welkhammer said she had been riding her bicycle nearby as the crane hit the buildings, and she saw the townhouse 'falling like a house of cards'.

People at the scene said they heard a loud explosion, smelled a strong gas odour and saw a thick yellow dust cloud. Cars were overturned and crushed, and rubble was piled several storeys high.

More than half a dozen buildings near the site had to be evacuated, and the Red Cross set up a shelter at a nearby school to help those who could not return home.

Firefighters with sniffer dogs scoured the rubble amid reports that people might have been trapped in the wreckage.

The 13 injured included at least three civilians, who were taken to hospitals in critical condition. One man was pulled from the debris nearly four hours after the accident. Four people - all believed to be construction workers - died.

Mr Christopher Bianchi, 40, owner of a Manhattan bar, said he saw three bodies on stretchers on the street.

'I saw them giving last rites,' he said. 'One of the policemen was giving last rites.'

New York Mayor Michael Bloomberg arrived at the scene hours later. 'It is a sad day,' he at a news conference. 'This accident is one of the worst the city has had.'

Many residents of the neighbourhood around the site said they had been worried for months about the possibility of a collapse.

They said the crane - looming higher each week - was a menace, particularly because so many residential buildings were being put up in the area with remarkable speed - several floors a week at times.

The cause of the accident on a sunny, windless day was unclear and under investigation by city, state and federal agencies.

But Mr Stephen Kaplan, an owner of the Reliance Construction Group working at the site, said a piece of steel had fallen and sheared off one of the girders holding the crane to the building.

A construction worker on the 15th floor, Mr Ismael Garcia, said he saw something fall and strike one or more of the girder ties, weakening or breaking the connections.

'Out of the corner of my eye, I saw a piece falling,' he said, and then the crane pulled away.

The task of raising the crane had city permission, and the crane had been inspected last Friday, with no violations found.

NEW YORK TIMES, ASSOCIATED PRESS, AGENCE FRANCE-PRESSE