A spokeswoman with a Thai agency that monitors the country’s airspace told AFP the plane also did not cross over Thailand.
A Beijing airport spokeswoman said the facility had activated an emergency response system. Screens at the airport indicated the flight was “delayed”.
An accident would be a huge blow for the carrier, which has bled money for years as its struggles to fend off competition from rivals such as fast-growing AirAsia.
It recorded its fourth straight quarterly loss during the final three months of 2013 and warned of a “challenging” year ahead due to intense competition.
The carrier admitted in 2012 it was in “crisis”, forcing it to implement a cost-cutting campaign centred on slashing routes and other measures.
In 2011, it chalked up a record 2.5 billion ringgit ($767 million) loss.
In July 2013, a Boeing 777-200 operated by South Korea’s Asiana Airlines skidded off the runway upon landing at San Francisco’s international airport after it clipped a seawall before touching down.
Three people died.
“We’re closely monitoring reports on Malaysia flight MH370. Our thoughts are with everyone on board,” the manufacturer said in a statement on its Twitter feed.
Boeing has been beset by problems with its high-tech 787 Dreamliners put into service two years ago, including a months-long global grounding over battery problems last year.
The information vacuum regarding the flight touched off a frenzy on social media, which saw an outpouring of concern for passengers and unconfirmed rumours that the plane had landed safely in southern China.
Malaysian Airlines has said those rumours were false, The Star newspaper reported.
A spokesman told the Sydney Morning Herald that Australian passengers were on board but could not confirm how many.
Malaysia Airlines (MAS) has suffered few accidents in its history.
One of its jets crashed in 1977 in southern Malaysia, killing all 93 passengers and seven crew.
A smaller Twin Otter aircraft, operated by its unit MASwings, crashed upon landing in Malaysia’s Sabah state on Borneo island last October, killing a co-pilot and a passenger.
There were no immediate signs of passenger relatives descending in large numbers on Beijing’s airport.
An AFP journalist saw one woman enter the arrivals zone at the airport and break down in tears. She was led away by police.
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