A total of 6,000 surgical masks have been lost at a hospital in Kobe, it was learned Tuesday. The Hyogo Prefectural Police is investigating the incident as a case of theft.

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

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

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

RELATED PHOTOS A drugstore in Tokyo runs low on masks in early February. | KYODO

Commuters, many with masks, walk along a sidewalk Tuesday in Tokyo. | AP