A total of 6,000 surgical masks have been lost at a hospital in Kobe, the capital of Hyogo Prefecture, western Japan, it was learned Tuesday.

The Hyogo prefectural police department's Fukiai station in the city is investigating the incident as a theft case.

The masks, worth 40,000 yen, had been kept at a machine room on the third floor of Japanese Red Cross Kobe Hospital, hospital officials said.

Four of the 12 boxes of masks were gone. Each box had 30 packages, which each contained 50 masks. The room is usually locked, the officials said.

A hospital employee noticed Thursday that some boxes were missing, and the hospital reported the incident to the police station on Monday.

The incident is "regrettable" although the hospital has enough masks for its staff, an official said.

The incident occurred at a time when Japan sees a shortage of face masks amid the continuing spread of the new coronavirus originating in China.

JIJI Press