The site where an explosion happened is seen in Utsunomiya, Japan, in this photo taken by Kyodo, Oct. 23, 2016. Kyodo/via REUTERS

Several explosions went off in on Sunday in two locations near a park in the Japanese city of Utsunomiya, killing one person and injuring three, state broadcaster NHK reported.

The cause of the blasts was not known, NHK said. The police said they were investigating whether the incidents at the two sites were linked, but did not give further details.

One of the injured people, a man, was being treated for shrapnel wounds, the broadcaster said. The person killed was also a man, but no other details were available about him or the other two wounded.

Crime rates are low in Japan, and there are no known groups waging any sort of violent campaign against the state.

Images broadcast by NHK showed two burnt out cars in a parking lot about 200 meters (650 feet) from the park and a charred broken bench at the edge of the park, where a folk art festival was underway.

Witnesses told the broadcaster they heard a series of loud explosions.