The last communication received from a Malaysia Airlines plane suggests everything was normal on board minutes before it went missing over the South China Sea, Malaysian authorities say.
Flight MH370 replied "All right, roger that" to a radio message from Malaysian air control, authorities said.
The search has been widened to waters off both sides of the peninsula.
Malaysia's air force chief has denied reports the plane was tracked to the Malacca Strait in the west.
The China-bound plane went missing on Saturday with 239 people on board.
It vanished about an hour after it took off from Kuala Lumpur International Airport, as it flew over the South China Sea, south of Vietnam's Ca Mau peninsula. No distress signal or message was sent.