The communications systems of missing Malaysia Airlines flight MH370 were deliberately disabled, Malaysia’s Prime Minister Najib Razak has said.

According to satellite and radar evidence, he said, the plane then changed course and could have continued flying for a further seven hours.

He said the “movements are consistent with the deliberate action of someone on the plane”.

The plane disappeared a week ago with 239 people on board.

The Kuala Lumpur-Beijing flight last made contact with air traffic control over the South China Sea to the east of Malaysia, about one hour after take-off.

Razak told a news conference that new satellite evidence shows “with a high degree of certainty” that the aircraft’s communications systems were disabled and then it changed course, flying back over Malaysia towards India.

Satellite signals continued to be picked up from the plane some seven hours after it lost radar contact.

Razak said the authorities are now trying to trace the plane across two possible “corridors” – north from the border of Kazakhstan and Turkmenistan through to northern Thailand, and south from Indonesia to the southern Indian Ocean.

The investigation, he said, had “entered a new phase”.