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Five others are injured

The cause is not known

(CNN) —  

A fire broke out Friday at a hospital in Fukuoka, Japan, killing 10 people and injuring five, a fire department spokesman said.

The fire at the orthopedics hospital started early in the morning and burned for roughly 2 1/2 hours.

Four of the injured suffered serious injuries, the spokesman said.

The cause of the blaze was not immediately clear.