(CNN) — The US Coast Guard extended the required safety zone surrounding active lava flows in Hawaii after a flying hunk of lava hit a tour boat and injured 23 people.

The so-called lava bomb punctured the roof of a lava tour boat named Hot Shot on Monday morning in Kapoho Bay on Hawaii’s Big Island, the Hawaii County Fire Department said.

Boats in Hawaii were already required to be at least 300 meters, or nearly 1,000 feet, away from lava flows at all times, the Coast Guard said. However, certain commercial and research vessels were granted special permission to approach closer.

These boats were allowed to be up to 100 meters (330 feet) away, and last week, the Coast Guard lowered that safety zone to 50 (164 feet) meters, according to Matthew West, a Coast Guard spokesman.

But in the wake of the lava bomb injuries, the Coast Guard said all boats must adhere to the 300-meter rule.

Hot Shot was one of the boats with special permission to approach closer, West said. The lava tour boats have operated in the area for at least 20 years, the Coast Guard said.

The Kilauea volcano erupted in early May, sending a smoldering flow of lava into residential areas on the Big Island. Kilauea was still erupting lava as of Sunday, according to the US Geological Survey.

‘Everyone was screaming and crying’

In video taken from the tour boat when the lava bomb struck, a loud noise can be heard and then passengers begin to scream.

A witness who saw the boat return said rocks were all over it, and some people had burns and gashes on their legs as they left the boat. One person was taken off on a stretcher.

Hilo Medical Center said it treated 13 passengers, and another 10 passengers with superficial injuries were treated on arrival at Wailoa Harbor.

Of the 13 who were injured, four went by ambulance to Hilo Medical Center, according to the Hawaii County Fire Department. A woman in her 20s was in serious condition with a fractured femur, the fire department said. The three others were in stable condition.

A first responder to the scene relayed what happened to one woman in a call with emergency dispatch.

“A piece of lava flew toward the boat; she closed her eyes, and the next thing she knew she felt pain to her left leg and to her lower back.”

Erin Walsh, who was on the boat with her boyfriend, told CNN affiliate KHON that they were oohing and aahing at the scene until the lava bomb surprised everybody.

“I didn’t even believe that this was coming toward us. We’d been watching it. It was so beautiful,” Walsh said. “Then it’s like, oh my God.”

The passengers began screaming and trying to find cover, Will Bryan, Walsh’s boyfriend, told KHON.

“There’s nowhere to go. You’re on a boat that’s so big. You’re just getting pelted. There’s no safe spot on the boat. You’re just getting hammered wherever you’re at,” Bryan said.

Walsh added, “Everyone’s trying to escape, so I just went to the middle of the walkway aisle, dropped to the ground, and was just covered in lava. It was crazy.”

A witness on another lava boat said that the explosion sent black sand everywhere and that the rocks on the boat’s roof were red hot.

“I saw the glow on top of the boat,” said the witness, who spoke to CNN on condition of anonymity.

About 50 rocks were on the boat, including three about the size of basketballs, the observer said. The witness’ boat approached the Hot Shot to help, and “everyone was screaming and crying.”

The lava bomb left a large hole in the boat’s roof, the fire department said. A railing was also damaged.

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