Seventy feet below ground is an array of goods that includes bricks of cocaine, fake taxi cabs used for covert operations, bomb-proof state cars and security files meant for the eyes of the CIA only - nice booty for potential looters.

As Brink's-Mat security vans brought out $200m (£137m) of gold from a safety store below 4 World Trade Centre, which was on the east side of the ruined complex, it emerged that someone had tried to get into the vaults, no doubt with robbery in mind.

Two weeks ago a security guard spotted scorch marks on a basement doorway which had not been noticed by a patrol team a few hours before. Behind the door were thousands of tonnes of gold and silver. It looked like someone had used a blowtorch and a crowbar and it prompted concerns that they may try to do so again. Video surveillance systems have now been installed.

As they dig amid the rubble, recovery workers are uncovering corridors and gangways that lead to the cavernous vaults below. The 16-acre basement has enough square footage to fill a building of greater proportion than the Empire State building. Engineers and recovery officials say that large parts of the underground storage rooms are undamaged.

Since September 11 very little has been said about the treasures that lie below what has become a mass grave. But down there are piles of old furniture, a mountain of Godiva chocolates, stacks of illegal assault weapons, as well as jewels and more gold and silver.

Beneath the customs house - 6 World Trade Centre - was a fleet of government vehicles, including dozens owned by the secret service. The cars were kept in a sealed-off area, part of which was a garage which housed a single armoured limousine used to carry heads of state and dignitaries visiting the city.

The building also housed an office of the CIA containing drugs, weapons and contraband seized by customs officers. The Bureau of Alcohol, Tobacco and Firearms also lost two evidence vaults, according to a spokesman.

"There could be several hundred weapons - somewhere between 200 and 400, ranging from small-calibre semi-automatic pistols to assault rifles," he told the New York Times.

He said agents plan to be on the scene when the remains of the building are demolished some time in the next two weeks. "After that, we'll be working at the landfill to search for any missing items."