A United Airlines jet returned safely to the Denver airport Tuesday after a bird struck one of its engines shortly after takeoff.

The engine that was struck continued to operate and the second engine wasn't affected, airline spokeswoman Megan McCarthy said. A passenger said the bird hit the right engine.

None of the 151 passengers and crew was injured.

The Boeing 757 had just left for San Francisco when the bird strike happened. McCarthy said the pilot's decision to return to the airport was a precaution.

A US Airways jet splash-landed in New York's Hudson River on Jan. 15 after a collision with a flock of birds knocked out both engines. All 155 aboard survived.

A passenger on the United flight, Frank Crowe, said "there was definitely panic but there wasn't hysteria" after the bird strike.

"We heard a large thump like we hit something, and the pitch of the engine changed dramatically to the point that it got real quiet, and there was a rattling, wheezing noise," Crowe said.

From the airport concourse after the plane landed, Crowe said he could see a dent on top of the engine cowling. He said mechanics climbed into the engine to inspect it.