Workers clearing rubble in a service tunnel underneath one of the collapsed World Trade Centre buildings found themselves surrounded by more than 100 armed FBI and secret service personnel, who had been tipped off by the owners where the gold was buried.

The collapsed buildings contained a number of vaults and strongrooms, but the police were not saying who owned the gold.

The Comex metals trading division of the New York Mercantile Exchange kept 3,800 gold bars — weighing 12 tonnes and worth more than $100 million (£70 million) — in vaults in the building’s basement. Comex also held almost 800,000 ounces of gold there on behalf of others with a value of about $220 million. It also held more than 102 million ounces of silver, worth $430 million.

The Bank of Nova Scotia, which kept gold in the Comex vault, reported $200 million of gold lost in the wreckage. Comex also held precious metals for Chase Manhattan Bank, the Bank of New York and Hong Kong and Shanghai Banking.

The vaults higher up the towers became burial chambers on September 11 as some workers tried in vain to protect themselves from the fire and smoke by taking refuge inside them.

The gold, which was discovered on Tuesday, was being transported through the basement of the building on the morning of September 11. Recovery workers reached a service tunnel and discovered a ten-wheel lorry and a number of cars which had been crushed by falling steel.

A temporary ramp was built to gain access to the tunnel and a small bulldozer was used to break through a wall. Then a team of police and firefighters arrived to put the gold into an armoured bullion lorry. Other workers were told to make themselves scarce. “If I tried to go down there they would have shot me,” one said.

Eight years ago, when the World Trade Centre was bombed by terrorists, more than $1 billion in gold was being kept in the basement vaults, the property of the Kuwaiti Government. The vaults withstood the blast.

At first police believed the terrorist attack was an attempted gold robbery. Since then the amount of gold kept under the World Trade Centre has been a carefully guarded secret.