An explosion of fire extinguishing bombs at a house in Kunming, Yunnan province, on Tuesday resulted in serious injuries to five men, Kunming Daily reported.

The police confirmed after a preliminary investigation that it was fire extinguishing bombs that caused the explosion. Fire extinguishing bombs are exclusively used to put out forest fires and unavailable for purchase by citizens.

Three of the five injured were reported to be out of danger.

Another three fire extinguishing bombs and some knives were also found in the house where the explosion happened.

The explosion is still under investigation.