Kuala Lumpur's ambassador to Beijing reportedly said during a meeting with Chinese relatives that the last radio transmission from the cockpit of missing Malaysia Airlines flight 370 was "Alright, good night".
Iskandar Sarudin was speaking to passengers' relatives and friends at a Beijing hotel.
A total of 153 of the 239 people on board the aircraft are Chinese.
The flight from Kuala Lumpur to Beijing disappeared from radar screens early on Saturday without making a distress call and no confirmed wreckage has been found, despite a vast search.
The "alright, good night" comment from one of the pilots came as the flight switched from Malaysian to Vietnamese airspace.