Honolulu, Hawaii — A tour helicopter burst into flames Monday morning after crashing nose-first onto a busy Kailua highway. Authorities believe three people were aboard the four-seat Robinson R44, all of whom were killed.

A woman driving on the street where the crash occurred initially thought the area was being bombed or an airplane had fallen. Melissa Solomon said she had turned onto another street because she was afraid pieces would fall on her car. One resident who heard the crash told CBS affiliate KGMB-TV that it sounded like the helicopter was making a strange noise.

"When it was falling, it wasn't on fire," Ikona Kaapana told KGMB-TV. "It was all black and there was no propellers and it was on its side when it was falling. We heard it land and it just went up in smoke."

Get Breaking News Delivered to Your Inbox

At least one car was damaged by the chopper's fuel tank. Debris from the crash littered nearby properties. While waiting for the fire department to arrive at the scene, bystanders used garden hoses to battle the blaze. Roads were temporarily closed as emergency personnel responded.

The FAA and the National Transportation Safety Board will investigate the crash. Authorities are unsure what caused the helicopter, operated by Novictor Helicopters, to come down. Novictor was involved in a previous crash last October, which resulted in two injuries after the pilot experienced a medical emergency.

Monday's crash marks the second such incident this month.