Billowing black smoke and orange flames poured from under the plane's wings, sending passengers fleeing.
NTSB sending team of three investigators to British Airways 777 engine fire that occurred in Las Vegas yesterday.— NTSB (@NTSB) September 9, 2015
A spokesman at McCarran International Airport says all 159 passengers and 13 crew members were able to get off the plane.
It was supposed to fly to London.
The 159 passengers and 13 crew members on board got off the plane, McCarran spokesman Chris Jones said.
Reggie Bgmncher, of Philadelphia, said she was charging her phone and waiting at a gate for her flight when she heard people saying, "Oh, my God." She looked out the window and could see "bursts of flames coming out of the middle of the plane."
"Everyone ran to the windows and people were standing on their chairs, looking out, holding their breath with their hands over their mouths," Bgmncher said.
The plane's emergency slides were deployed a few moments later and passengers quickly got off the plane. She said it was a "bit more orderly" than she would have expected given the dramatic nature of the fire and smoke.
Firefighters stationed at the airport reached the plane two minutes after getting reports of flames, and within another three minutes, everyone inside the plane had escaped.
After firefighters extinguished the flames, emergency vehicles could be seen surrounding the aircraft, which was left a sooty gray from the smoke and fire retardant.
Federal Aviation Administration spokesman Ian Gregor said the plane's left engine caught fire and an investigation was underway. The National Transportation Safety Board was collecting information about the incident, said Eric Weiss, a spokesman for the agency in Washington.
Clark County Deputy Fire Chief Jon Klassen said the cause of the fire wasn't clear yet, but the fire didn't appear to breach the cabin.
One of the airport's runways was shut down, but operations continued on the other three runways, officials said.
The Boeing 777-200 was bound for Gatwick Airport near London.
British Airways spokeswoman Caroline Titmuss didn't answer questions about the incident in an email exchange but said "safety is always our priority."
Titmuss said in an email that the airline was "looking after customers" but didn't elaborate. She said the airline would release more information later.
Las Vegas' airport is the ninth-busiest in the U.S. and had nearly 43 million passengers last year. The airport has been taking steps to accommodate more international travelers seeking direct flights to Europe and Asia, including adding new gates to accommodate wide-body double-decker jets.