The alarm was only raised when smoke was discovered to be coming from the garage by people living nearby on Monday.

Police spokesman Thomas Neuendorf said the 30-meter (100-foot) tunnel leading to the deposit room came from an underground garage near to the Berliner Volksbank in Berlin's Steglitz district.

Neuendorf told the AP news agency that the passageway - elaborately constructed and with ceiling supports - was "very professional" and that it would have taken months or weeks to complete.

Several safety deposit boxes were forced open, although the value stolen in the heist was initially unclear to police.

The perpetrators apparently set a fire to destroy any evidence that might identify them before leaving through the tunnel.

"It might take some time to investigate the damage," said a spokeswoman for the Berliner Volksbank.

It's not the first time Berlin has seen an audacious bank robbery. Four robbers took 16 people hostage in the neighboring district of Zehlendorf in 1995 and escaped through a tunnel they had dug previously.

A nine-hour hostage drama in December, also in Zehlendorf and involving a bomb threat and some 300 police, ended when the robber surrendered. Police found the bag of "explosives" the man was using to threaten staff contained nothing but flour.

rc/dr (AP, AFP, dpa)