SHANGHAI - Experts have raised questions about Malaysia Airlines' slow response after one of its planes went missing over the South China Sea while flying from Kuala Lumpur to Beijing.

They point out that there was a time lag of several hours, after contact was lost with the missing aircraft, before any credible information surfaced.

International guidelines require that an airline should publish information within 30 seconds of losing contact with a flight, according to Zhang Qihuai, associate chairman of the Aerial Law Study Institution of Beijing Legal Study Association.

The Boeing 777-200 aircraft left the Malaysian capital at 12:41 a.m. (Beijing Time) on Saturday, and was expected to land in Beijing at 6:30 a.m. the same day.

It was carrying 227 passengers, 153 of them Chinese.

Contact was lost with the plane at around 2:40 a.m. (Beijing Time) but it wasn't until 7:30 a.m. that Malaysia Airlines announced the plane as missing, Zhang was quoted as saying by Xinhua.

"It is a rare case," another anonymous industry official was quoted as saying in the Xinhua report.

Planes are equipped with several communication devices, which function simultaneously, he said.

Even if all fail to work, the plane can be located through radar code.

"Only under extreme conditions will a flight be out of contact," he said, adding that it is unlikely such a scenario would occur even if the plane was hijacked or went through a natural disaster.