Armed robbers have targeted a bank in the Italian city of Naples – holding 25 people hostage before escaping through a tunnel.

Hundreds of safety deposit boxes were ransacked by the gang, meaning the exact value of the theft remains unclear at this stage.

The incident unfolded at a branch of Credit Agricole on Thursday morning – and the hostages were held for a couple of hours prior to their release.

Footage posted online showed firemen smashing through windows to help people climb out, and no injuries have been reported.

Reports suggest the robbers may have escaped through sewers after drilling a hole in the bank’s floor throughout the night.

Detectives are now searching sewers throughout the local area but are yet to make any arrests.

According to local media reports, three or four people were involved in the heist – and had worn masks depicting famous actors.

One hostage told Fanpage.it that customers and bank staff were locked in a room. They added that, although the thieves were armed, no violence was used.

Dozens of customers descended on the bank last night to demand information.

One told La Repubblica: “We want to know what was stolen. Was the bank vault containing the cash stolen, or were private safety deposit boxes emptied? How many safe deposit boxes were opened?”

The company that manages Naples’s water network has been inspecting the sewer system, according to the local news site Fanpage.it.

It was unclear whether the robbers managed to flee with any loot. According to Fanpage, the robbers were believed to have targeted safety deposit boxes and there was no cash inside the bank.

The Naples prosecutor Nicola Gratteri was also at the scene.

One of the people held hostage, a bank customer, told Fanpage they had been locked in a room. “I was in the bank when they entered; there was definitely three of them. They came and locked us – customers, employees and the manager – in a room. They were armed but they didn’t use violence.”