Lava explosion near Hawaii tour boat injures at least 23

At least 23 people were injured in Hawaii on Monday after a lava explosion from the Kilauea volcano sent debris flying through the roof of their tour boat.

The "lava bomb" hit the roof of the Lava Ocean Tours vessel near the town of Kapoho, Hawaii's Department of Land and Natural Resources said. The explosion sent lava through the boat's roof and into the passenger cabin.

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At least four passengers were rushed to the Hilo Medical Center, according to the Hawaii County Fire Department. Two of those hospitalized were in stable condition while one woman was in serious condition with a fractured femur.

Nine other passengers drove themselves to the hospital, and officials considered their injuries to be superficial. Later Monday, officials added that 10 other passengers were treated at the harbor, raising the number of injured to 23.

The boat returned to the Wailoa Sampan Basin Harbor in Hilo around 7 a.m., following its 4 a.m. departure. The entrance to the Pohoiki Boat Ramp, from which the tour departed, is now located half a mile away from the active ocean entrance, officials said.

Kilauea volcano eruption

A "tiny new island" has formed along the coastline of the Kilauea volcano, the U.S. Geological Survey said Friday. Officials believe it's "part of the fissure 8 flow that's entering the ocean."  (U.S. Geological Survey)

Lava Ocean Tours did not immediately provide comment to Fox News.

Shane Turpin, the owner and captain of the boat that was hit, said he never saw the explosion that rained down on his boat. He noted the tour group had been in the area for roughly 20 minutes making passes of the ocean entry about 500 yards offshore.

Turpin didn't observe "any major explosions," so he navigated the vessel closer, to about 250 yards away from the lava.

"As we were exiting the zone, all of a sudden everything around us exploded," Turpin told The Associated Press. "It was everywhere."

He added that he has been observing and documenting these explosions and that this type of activity is new. There were no warning signs before the blast, according to Turpin.

After the explosion, those in the tour group quickly pulled together to help one another, Turpin said. 

"What I saw in humanity this morning was amazing. I mean this was a group of people that never met before, and they were brought together," he said. "In all honesty, we definitely evaded a catastrophic event today."

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Lava continues to spew from fissure 8 of the Kilauea volcano since its initial eruption on May 3rd. The U.S. Geological Survey on Sunday alerted that the volcano was under its "warning/orange" advisory, meaning a "major volcano eruption is imminent, underway, or suspected."

"tiny new island" has been formed along the coastline, which the agency said Friday was "most likely part of the fissure 8 flower that's entering the ocean." The island is believed to be roughly 20 to 30 feet in diameter. 

Fox News' Mike Arroyo, Jeff Paul and The Associated Press contributed to this report.

EDITOR'S NOTE: An earlier version of this report stated that a different tour company operated the boat, citing emergency officials who later issued a correction.

Nicole Darrah covers breaking and trending news for FoxNews.com. Follow her on Twitter @nicoledarrah.