Prime Minister Lee Hsien Loong has said in a tweet on Saturday that his "thoughts and prayers" are with the passengers and crew of a Malaysian Airlines flight that has gone missing, as well as their families.

The aircraft which left Kuala Lumpur more than 12 hours ago for Beijing, China has still not been located, the airline said.

PM Lee said in his tweet: "Heard abt @MAS aircraft missing, on a flight from KL to Beijing. Our thoughts & prayers are with the passengers & crew, & their families."

MAS said in a statement that the passengers were of 14 different nationalities. There were no Singaporeans on board. More than six in 10 were China nationals. There were also 38 Malaysians and 12 Indonesians on board.

The rest of the passengers were from Australia, France, America, New Zealand, Ukraine, Canada, Russia, Italy, Taiwan, Netherlands and Austria.