The tail of the missing AirAsia plane has been found underwater in the Java Sea, according to Indonesian officials.

The find is vital because the cockpit voice and flight data recorders, or black boxes, are located in the aircraft's tail, and will be crucial to investigators trying to establish why the plane crashed.

"We have successfully obtained part of the plane that has been our target," search and rescue agency chief Bambang Soelistyo said.

"The tail portion has been confirmed found."

The section of plane was identified using an underwater remote operated vehicle.

Flight QZ8501 came down on 28 December during a storm en route from Indonesia's second city Surabaya to Singapore.

Before take-off, the pilot had asked to fly at a higher altitude to avoid the storm, but permission was denied because of the number of planes above him on the busy route.

Forty bodies and debris from the plane have been recovered from the surface of the waters off Borneo, but strong winds and high waves have prevented divers from reaching larger pieces of suspected wreckage detected by sonar on the sea floor.

It is thought to include parts of the fuselage, where many of the bodies of victims may still be trapped.

In his last communication, Captain Iriyanto, an experienced former air force pilot, said he wanted to change course to avoid the storm system.

Soon after all contact was lost, about 40 minutes after the Airbus A320-200 had taken off.

Of the 162 passengers and crew on board, 155 were Indonesian and three South Korean. The other four were from Singapore, Malaysia, Britain and France.

Following the disaster, Indonesia has reassigned some airport and air traffic control officials who allowed the flight to take off, and has tightened rules on pre-flight procedures.

The authorities in Jakarta have also suspended all AirAsia flights between Surabaya and Singapore - the route where the plane went missing - after it emerged the aircraft had not been authorised to fly on the day it came down.

The budget airline was not permitted to make the journey on Sundays, although the transport ministry said this had no bearing on the accident.