The Royal Malaysian Air Force (RMAF) scrambled a search aircraft at around 8am, soon after Malaysia Airlines reported that its plane was missing, Malaysian sources told CNN.
The aircraft took off before authorities corroborated data indicating that the plane turned back westward, a senior Malaysian government official told CNN.
But the air force did not inform the Department of Civil Aviation or search and rescue operations until three days later, March 11, a source involved in the investigation told CNN.
CNN also learnt that MH370's pilot, Captain Zaharie Ahmad Shah, was the last person on the jet to speak to air traffic controllers, telling them "Good night, Malaysian three-seven-zero."
The sources said there was nothing unusual about his voice, which betrayed no indication that he was under stress.
One of the sources, an official involved in the investigation, told CNN that police played the recording to five other Malaysia Airlines pilots who knew the pilot and co-pilot.
"There were no third-party voices," the source said.
Flight MH370 disappeared from military radar for about 120 nautical miles after it crossed back over the Malaysian Peninsula, sources say. Based on available data, this means the plane must have dipped in altitude to between 4,000 and 5,000 feet, a senior Malaysian government official and a source involved in the investigation tell CNN.
The dip could have been programmed into the computers controlling the plane as an emergency manoeuvre, said aviation expert David Soucie.
"The real issue here is it looks like - more and more - somebody in the cockpit was directing this plane and directing it away from land," said CNN aviation analyst and former National Transportation Safety Board Managing Director Peter Goelz.
"And it looks as though they were doing it to avoid any kind of detection."