At least 23 people were injured on Monday when flying lava from the Kilauea volcano struck a tour boat in Hawaii, officials have said. The debris crashed through the roof of the vessel, which had taken visitors to watch the lava flowing into the sea.

A passenger has suffered a broken thigh bone, AP quoted the Hawaii County Fire Department as saying. Three others were in a stable condition with unspecified injuries. Many other passengers suffered superficial burn injuries and were being treated.

Shane Turpin, owner and captain of the boat, said the tour group had been in the area for 20 minutes, around 450 metres offshore, before heading closer to around 230 metres to see the lava. “As we were exiting the zone, all of a sudden everything around us exploded. It was everywhere,” he said.

Official warnings have asked tour boats to stay away from the lava entering the ocean as it can create clouds of acid and fine glass. Despite the dangers, many companies continue to operate the vessels.

Kilauea, an active volcano, has continuously erupted for 35 years. In May, it entered a fresh phase of eruption after new fissures were formed in a residential neighbourhood.

Afterwards, the US Coast Guard instituted a safety zone, prohibiting vessels from getting closer than 300 metres from the ocean-entry points. However, experienced tour operators with special licences are allowed to get as close as 50 metres to where the lava flows into the sea.