(Reuters) - A China Eastern Airlines (600115.SS) Boeing 737-800 with 132 people on board crashed in mountains in southern China on Monday after a sudden plunge from cruising altitude at about the time when it would normally start to descend ahead of its landing.

Media said there were no signs of survivors on the domestic flight.

The airline said it deeply mourned the passengers and crew, without specifying how many people had been killed on the jet, an earlier model to the 737 MAX with a strong safety record.

Boeing (BA.N) said it was ready to assist China Eastern and was in contact with U.S. transportation safety regulators over the incident.

Chinese media carried brief highway video footage from a vehicle's dashcam apparently showing a jet diving to the ground behind trees at an angle of about 35 degrees off vertical. Reuters could not immediately verify the footage.