A witness said she was walking across the Aurora Bridge in Seattle just after a charter bus and a Ride the Ducks vehicle collided. She soon came upon a mess of jumbled metal and glass.

Related: 4 people killed, more than 50 injured in crash

Jahna Dyer, a registered nurse, said that some victims were sprawled out on the pavement while others milled about seemingly in shock and falling down.

KIRO Radio Reporter Josh Kerns heard similar reports from the scene.

“Seeing the shock on the faces of dozens of Chinese students when they came off the bridge after the crash is something I’ll never forget,” Kerns said. “You can tell they went through something horrendous. When I tried to talk to them, most of them couldn’t even speak, let alone respond at all.”

The charter bus was reportedly carrying international students and teachers from North Seattle Community College.

Authorities say four people were killed in the crash and more than 50 people were injured. Dyer said she stabilized the neck of an injured man and helped a woman who had a cut lip and glass in her eye.

Another witness, John Mundell said he was at the south end of the bridge when he heard a screech and the twisting of metal and soon saw what appeared to be a few dozen people on the ground.

Mundell said he wanted to help the injured, but “felt helpless.”

Kerns spoke with one driver who was directly behind the Duck vehicle when the crash happened.

“They suddenly saw the Duck boat swerve violently and slam into the side of that tour bus,” Kerns said. “As they slowly drove past &#8212 what she thought first was a blowout &#8212 she saw a big piece of the front steering column there. So perhaps it was a mechanical malfunction of some kind.”

Kerns said that the scene will not be cleared for hours, cutting off a major arterial in Seattle.

“The steady stream of ambulances has finally stopped and they seem to be slowly moving from that rescue scene, to something more stabilized for an investigation,” Kerns said. “The bridge is going to be closed all day long into the evening, and maybe overnight.”

The Associated Press contributed to this report.