ABC News

ABC News John Schriffen reports:

A Berlin-bound United Airlines flight landed safely at Newark airport this weekend after the aircraft experienced a "mechanical issue with the engine," officials said.

United Airlines flight 96 left Newark at 5:50 p.m. and was carrying 173 passengers and crew Saturday when a tire burst and the debris was sucked into one of the plane's engines, according to reports.

Witnesses on the ground said they saw fire coming from the engine as they watched in suspense.

"I ran to the window, looked outside, saw the airplane and saw fire coming out, " D'Jenaba Johnson Jones said.

"As it was elevating I noticed that there was a flame spitting out of the left engine it was kind of going like pop-pop- pop-pop," said Alex Jackson.

The Boeing 757 immediately turned around, back for Newark. For two hours and 15 minutes the plane circled, burning off fuel.

"This can be quite disturbing if you're sitting in the cabin and not understanding what goes on because it's actually shooting what looks like fireballs out the front of the engine," ABC News aviation consultant Steve Ganyard said.

The plane landed safely at 8:10 p.m.

"The crew followed standard procedures in returning to Newark, where the airplane landed safely," United Airlines officials said in a statement Saturday.