Cologne, Germany - Salvage work at a German archives which collapsed this year, destroying 1,000 years of history, has halted because of underground water, the fire brigade in Cologne said Wednesday.

A giant pothole formed under City of Cologne archives and caused its sudden collapse on March 3. For four months, papers and parchments have been sifted from rubble pulled out of the hole by excavators.

The excavators have now reached a point two metres below the water table.

"We've got to a point where we can't do any more or else we'd have a washout," said fire spokesman Daniel Leupold. Engineers are to suggest next month some other way of recovering the deep, wet debris.

Archives officials calculate 90 per cent of the archives' contents have been recovered. Some are just dusty or torn, others unuseable.

The collapse is one of Germany's worst cultural losses since the firestorms of the Second World War.

"We are now 12 metres below street level," said Leupold. Engineers believe the deepest debris is 20 metres down. The city of Cologne is built on bank of the Rhine river.

Leupold said the alluvial sand and gravel would collapse if the excavators simply pumped out the water and dug deeper.

There have been estimates it may cost a billion euros to repair the damaged papers and put up a new building.

Prosecutors and municipal officials are studying who is to blame and if they can be sued.(dpa)