An emergency earthquake warning sent to millions of people in Japan caused a brief panic on Friday(Jan.05) and disrupted Tokyo's transport network.

But the loud alert, which was sent to millions of mobile phones, turned out to be a false alarm triggered by an error in the earthquake warning system.

"An earthquake has occurred off the coast of Ibaraki," the message read. "Prepare for strong jolts."

Train services were suspended but there were no reports of injuries or damage.

Officials believe the alert, sent by the Japan Meteorological Agency, was caused by the early warning system misreading two minor earthquakes as one larger one.