KĀʻANAPALI (HawaiiNewsNow) – First responders treated several people following an explosion at a West Maui resort Thursday evening.

It happened at around 6:15 p.m. at The Whaler on Kāʻanapali Beach, located at 2481 Kāʻanapali Parkway.

Web cam video shows debris shooting from the building.

Bystanders with medical and first responder backgrounds assisted police until medics and firefighters arrived.

Seven people, ranging in age from 18 to 74, were hurt, according to Maui police. Three suffered critical injuries and one was flown via medevac to Maui Memorial Medical Center’s emergency room.

“We were swimming down at the pool at the Sheraton and suddenly there was this huge, earth-shaking boom. You can tell it wasn’t like a firework or something somebody planned,” said David Flint.

“We know it’s a real crowded area and it was pretty scary. There were all sorts of rumors right away. Somebody was saying a grill exploded, somebody else said there was a bomb in a garbage can. It was definitely surreal,” Flint said.

Debris was still scattered all along the beach late into the night, and investigators put up yellow flags to mark them.

Preliminary investigations suggest that the explosion may have involved liquefied petroleum gas, which supplies common area BBQs, police said. Witness statements indicate a possible grill malfunction before the incident.

The official cause remains undetermined and is under active investigation.

No evacuations were necessary and there was no additional threat, police said.