For months, acrid clouds of smoke from the site could be smelled several miles away in Brooklyn and upper Manhattan. The fires, fuelled by documents and office furniture, had been so strong they needed a near-constant jet of water sprayed on them.

"You couldn't even begin to imagine how much water was pumped in there," said Tom Manley, a firefighters' union representative. "It was like you were creating a giant lake."

At times, the flames slowed the work of clearing the site. Flare-ups would occur from time to time as demolition and rescue crews exposed the debris to the air.

But for the 75 firefighters at the site daily, working without the flames only makes the job of finding human remains a bit easier.

"It'll be a lot less of a hindrance now since the smoke's not there," Mr Manley said. "But the emotional state stays exactly the same. Just being down there is emotional."

Clearing the site is expected to take another six to nine months, with work focussing on the seven floors of compacted rubble underground.

Small hot pockets continue to be discovered and a fire engine remains on standby at the site. Though the flames are out, the New York fire department still considers Ground Zero an active fire scene.