A blast ripped through an abandoned one-storey government building near here early on Thursday morning, just a shout away from a police camp set up a year ago to monitor illegal stockpile of explosives in the area.

The Trinamul Congress has alleged that the explosion was caused by crude bombs stored by BJP workers at the building in Danrka. The police camp was established after a blast had killed eight persons while making crude bombs just a kilometre away in 2017.

The building was part of a primary health centre which no longer functioned.

Birbhum district police chief Shyam Singh said a probe had started into the explosion. “The forensic department and bomb squad have been asked to find out the nature of explosives. Nobody has been arrested so far,” he said.

The health department has lodged a police complaint and ordered a probe to find out how its premises were used by suspected miscreants to keep bombs.

Sources said the explosion had occurred around 3am on Thursday. The building had three small rooms and they all collapsed. The debris flung over 20m away, damaging roofs of two nearby houses.

It was found out that hundreds of wooden logs had been stored inside the building.

The health centre, which had been set up in the 1970s, was abandoned following the construction of a new building a few years ago.

Villagers said although there was a police camp, the abandoned structure had become a den of criminals. The camp operates out of another building of the defunct health centre.

“I was sleeping at my house when we heard a loud bang. A concrete chunk landed on our tin roof and the ceiling fan fell off, injuring my father. We panicked,” said Meherunnesa Khatun, a Class XII student, whose house is 10m away from the explosion site.

The sources said four police personnel were deployed at the camp round the clock.

Sheikh Abul Hossain, a Trinamul worker and a resident of Danrka, said: “It is completely the police’s failure. The police camp was set up to prevent such incidents. This time, the explosion took place next door to them and they knew nothing about it.”

Birbhum Trinamul chief Anubrata Mondal said BJP workers had kept crude bombs inside the building secretly and that was why the police didn’t know it.

Trinamul Congress workers blocked the nearby road, demanding the removal of Chayam Ghosh, the officer-in-charge of the police camp, and accusing BJP supporters of stockpiling bombs at the government building.

Biswajit Mondal, the district vice-president of the BJP, said: “It is ridiculous to blame the BJP. The police personnel at the camp used to allow Trinamul men into the building. We think the bombs were kept there by Trinamul workers with prior permission of the police.”