The fires that have been burning in the ruins of the World Trade Center since the 11 September terror attacks have finally gone out, officials say.

"We consider the fire to be out," said Fire Department spokesman Robert Calise. But he warned it was possible that some small fires could still be burning.

Firefighters will remain on hand in case of flare-ups

For more than three months the fires had sent up plumes of acrid smoke that could be smelt from several kilometres away in upper Manhattan and Brooklyn.

Fire engulfed the World Trade Center when two fuel-laden hijacked planes slammed into the twin towers, killing more than 3,000 people. The flames were fed by documents and office furniture lying in the debris.

Ongoing danger

As rescue and salvage crews picked their way through the rubble of the collapsed buildings they would frequently expose the fires to oxygen, causing flare-ups.

Danger from the flames frequently delayed the rescue efforts.

For months the fires were sufficiently strong that they had to be controlled with a constant spray of water from fire trucks.

Even now a fire truck will remain on standby at the site just in case, Mr Calise said, as it is still possible the fires could be reignited when debris is moved and oxygen fans into the hot remains deep underground.

Memorial plans

It will be months before every piece of debris has been removed and the chances of any new fires can finally be ruled out.

But the BBC's Jane Standley in New York says people there will welcome the news, as it is a sign of some clear progress in the vast job of clearing the mountain of rubble.

On Sunday the last remaining standing facade of the twin towers, a 15-metre high steel section, was brought down.

Officials said the fragment - part of the 110-storey north tower - would be saved for a possible future memorial.

A section of the south tower, removed several weeks ago, has also been saved.