A similar raid was carried out last weekend in central Paris
For the second time in a week, robbers in Paris have dug a tunnel to access the vaults of a high-street bank.
Police said they may have used the sewerage network to enter the BNP Paribas bank from a metro station, but fled before they could steal anything.
It is the latest of several similar incidents in the city.
A week ago, thieves raided dozens of safety deposit boxes at a branch of Credit Lyonnais after digging a tunnel into the vault.
Last weekend's underground raid on a branch of the Credit Lyonnais seems to have whetted the appetite of other would-be bank robbers, says the BBC's Hugh Schofield in Paris.
Once again the gang dug a tunnel from the sewerage system, to gain access to the basement of the bank in the 13th district near the Tolbiac underground station.
But on this occasion, after smashing a hole in the wall at about 0400 (0200 GMT), the robbers set off an alarm.
Police were quickly on the scene, and there was a small explosion possibly caused by a ruptured gas main, our correspondent adds.
In the confusion, the robbers escaped, but empty-handed.
In last weekend's more successful raid, the robbers spent a night undisturbed in the bank vault and left with an undisclosed amount of cash and jewels.