AT least 22 people have been injured and four rushed to hospital after a lava bomb crashed through the roof of a tourist boat off Hawaii.

The Lava Ocean Tours boat was travelling along the coast of the Big Island when molten rock the size of a basketball crashed into the vessel, causing lava to spill through the boat and leaving a gaping hole in the canopy.

Shocked passengers of a nearby tourist boat captured vision of the havoc, as the boat retreated to the safety of Wailoa Harbor.

Three of the four people who were taken to hospital are in a stable condition.

One 20-year-old woman who was on board is in a serious condition and suffered a fractured femur.

Other passengers suffered minor injuries including burns, scrapes and superficial injuries.

Sightseeing boats normally tour the other side of the island, but recent activity from Mt Kilauea caused a change in the boats usual route.

Hawaii’s Department of Land and Natural Resources will investigate if the tour boat strayed outside the US Coast Guard established safety zone.

Boats are generally barred from encroaching within 300 metres of lava ocean hot-spots.

Mt Kilauea began erupting in May, sending smouldering lava into homes.

So far, up to 700 properties on the island have been destroyed.