HILO, Hawaii - UPDATE:

23 people were injured after a lava bomb exploded and punctured the roof of a tour boat off the Big Island Monday morning.

Hawaii County Civil Defense reports that an explosion at the ocean entry hurled lava bombs and debris onto a lava tour boat.

Four passengers were taken by ambulance to the hospital, one seriously injured with a fractured femur.

The Department of Land and Natural Resources (DLNR) says the tour boat involved in this incident is a Lava Ocean Tours vessel. The tour boat returned to the Wailoa Boat Harbor in Hilo around 7 a.m. with 12 injured passengers, according to the Hawaii County Fire Department. Three of the victims were rushed to the Hilo Medical Center by ambulance. Two are listed in stable condition and one woman is listed in serious condition due to a fractured femur, according HFD. The nine others who were injured drove themselves to the hospital with what the fire department calls "superficial" injuries.

The Hawaii County Fire Dept. says a railing on the tour boat was also damaged by the lava bomb. It's unclear how many people were on the boat or how close it was to the lava. However, passengers reported to DLNR's DOCARE officers that the tour boat was outside of the safety zone established by the U.S. Coast Guard.

The exact location and time of the incident is unclear. But DLNR says tour boats typically depart from the Wailoa Boat Harbor in Hilo around 4 a.m. Prior to the lava eruptions in the Lower East Rift Zone, tours left from the Pohoiki Boat Ramp, which is located about half a mile from where lava is entering the ocean.

This is a developing story and will be updated.