One man has been killed and three other people injured when two explosions rocked a park in Utsunomiya, a city in Japan's Tochigi prefecture.

Cars in the parking area were seen burning as police and emergency personnel arrived at the scene.

There was a festival underway in the park when the explosions occurred.

The first blast took place about 11.30am local time and within a minute there was another explosion.

A badly disfigured body was discovered at the parking space.

Japan's state broadcaster NHK quoted an eyewitness who said he heard a loud sound and saw three people lying on the ground. He added that he could smell gunpowder at the blast site.

The cause of the explosions is not known.

A suspected suicide note has reportedly been found at the blast location inside a vehicle, which belonged to a 72-year-old former officer in Japan's Self-Defense Forces – the country's combined military services.

Photos showing charred vehicles from the explosions have been posted on social media.

Utsunomiya is located north of Japan's capital Tokyo.

Japan twin explosions Utsunomiya
Firefighters investigate a burnt-out car at the site of an explosion in Utsunomiya, Japan Kyodo via Reuters