PRAGUE (AP) — Explosions in a Czech machinery plant injured a total of 19 people with three of them in critical condition, officials said on Thursday.

Police spokeswoman Hana Kaizarova said the first explosion occurred around 11 a.m. (1000 GMT) in a production hall and a number of others followed, making it difficult for rescuers to access the site in the Policske Strojirny A.S. near the town of Policka, some 150 kilometers (95 miles) east of Prague.

The company that ran the plant, which also processes old ammunition, did not comment. Kaizarova said it was not immediately clear what material exploded. She said authorities have not discovered any fatalities.

 The regional government in the nearby city of Pardubice said an unknown explosive in a tank detonated first, triggering the other explosions.

Pavel Svoboda, the head of the regional rescue service, said three people suffered serious injuries, mostly burns, and were in critical condition. They were transported by helicopters to hospitals.

Svoboda said four rescuers were injured.

Authorities have warned the public to avoid the area.

In 2015, a huge explosion of 320 metric tons (353 tons) of gunpowder in the same factory injured two workers.