The museum left the safe open so that visitors could touch the gold

The gold bar, valued at $1.71m (1.27m euro; £0.87m), weighed about 220 pounds (100kg) and was kept in an open safe.

The museum, in the central city of Takayama, said the gold was not protected by sensors as they wanted visitors to be able to touch it.

But the group of thieves went one step further, helping themselves to the precious metal and dragging it away.

The gold was lugged past an employee alerted by the noise, down a staircase and out of the museum where the three men were driven away by a fourth accomplice.

"The gold was exhibited on the second floor, which was monitored by a security camera from the first floor," said 59-year-old Hisao Nakahagi, the owner of the gold.