A Boeing 737 carrying 132 people crashed early Monday in China. Although Boeing's 737 has faced extraordinarily high-profile safety concerns over the past three years, the plane that crashed Monday was a different version of the aircraft than the embattled 737 Max that shook Boeing to its core.

The cause of Monday's crash has yet to be determined. The plane had been in service since 2015. The flight, operated by China Eastern Airlines, was flying from the southwestern Chinese city of Kunming to Guangzhou when it crashed.

Thousands of firefighters, police officers and paramilitary troops assembled Tuesday to search for any survivors of a passenger plane that crashed into a steep, heavily wooded site in southern China.

The Boeing 737 plane, operated by China Eastern Airlines, went down Monday afternoon in the Guangxi region, and flames and smoke could be seen rising from a hillside, Chinese news reports said, according to pictures and videos shared from the scene. The fire was put out later Monday.

“The situation with casualties remains unclear,” said an online report issued by Chinese state television.