Five children were injured in Austria when a “wartime relic” beneath their campfire exploded, the authorities there said on Sunday.

The object was under the firepit when it exploded about 8 p.m. local time Saturday, according to a police statement. The accident happened in the Freistadt district, an area in the northern state of Upper Austria, the statement said.

Melanie Kleiffner, a police spokeswoman, said on Sunday that investigators believed that the relic likely dated from World War II, but that it was not possible to provide more definitive information while the investigation was ongoing.

Ms. Kleiffner said the children had been attending a youth camp in the town of St. Oswald Bei Freistadt when the accident happened.

“They were sitting around the fire, enjoying their time, and suddenly it exploded,” she said in a telephone interview, adding that they had spent around an hour in the area before the explosion without incident.

The injured children, whose ages ranged from 10 to 14, were taken to a children’s hospital in the city of Linz for further treatment, the police statement said. The five children were released from hospital on Saturday after being treated for minor injuries, Astrid Petritz, a spokeswoman for Kepler University Hospital, said. “They were lucky. There were no heavy wounds,” she added.

Officers at the scene of the explosion later identified a second wartime relic at a nearby firepit. The police said a team of bomb disposal experts was attending the scene.

Local officials have closed the area immediately surrounding the firepits until Monday to allow for further investigation, Ms. Kleiffner said.

It is not uncommon for unexploded bombs from 20th-century conflicts to be uncovered in Austria, though accidents like this appear to be rare.