Flight QZ8501 vanished from radar screens over the northern Java Sea on Dec. 28, less than half-way into a two-hour flight from Indonesia's second-biggest city of Surabaya to Singapore. There were no survivors among the 162 people on board.
"We've found the tail that has been our main target," Fransiskus Bambang Soelistyo, head of the search and rescue agency, told a news conference in Jakarta.
The tail was identified by divers after it was spotted by an underwater machine using a sonar scan, Soelistyo said. He displayed underwater photographs showing partial lettering on the sunken object compared with a picture of an intact Airbus A320-200 in AirAsia livery.
"I can confirm that what we found was the tail part from the pictures," he said, adding that the team "now is still desperately trying to locate the black box".
Indonesia's Minister for Maritime Affairs, Indroyono Soesilo, told another news conference: "With the finding of the tail, six SAR (search and rescue) ships are already at the location to search within a radius of two nautical miles."
Forty bodies and debris from the plane have been plucked from the surface of the waters off Borneo, but strong winds and high waves have been hampering divers' efforts to reach larger pieces of suspected wreckage detected by sonar on the sea floor.
Locating the tail has been a priority because the cockpit voice and flight data recorders that can provide vital clues on why the plane crashed are located in the rear section of the Airbus.
"I am led to believe the tail section has been found,"AirAsia boss Tony Fernandes tweeted minutes after the announcement.
"If (it is the) right part of tail section, then the black box should be there ... We need to find all parts soon so we can find all our guests to ease the pain of our families. That still is our priority."
In Pangkalan Bun, the southern Borneo town closest to the crash site, search and rescue agency coordinator Supriyadi told reporters the bad weather that has dogged the operation for 10 days had abated and divers were in the water.
But, as ships with acoustic "pinger locators" designed to pick up signals from the black box converged on the scene of the find, he cautioned the tail section of the aircraft might not be fully intact.
"The location of the tail is relatively far from the point of last contact, about 30 km (20 miles)," he said.
"The black box is located behind the door, to the right of the tail. There is a possibility that the tail and the back of the plane are broken up."
Until investigators can examine the black box recorders the cause of the crash remains a mystery, but the area where the plane was lost is known for intense seasonal storms. BMKG, Indonesia's meteorological agency, has said bad weather may have caused ice to form on the aircraft's engines.
Indonesia AirAsia, 49 percent owned by Fernandes's Malaysia-based AirAsia budget group, has come under pressure from the authorities in Jakarta since the crash.
The transport ministry has suspended the carrier's Surabaya-Singapore license, saying it only had permission to fly the route on Mondays, Tuesdays, Thursdays and Saturdays. Flight QZ8501 took off on a Sunday, though the ministry said this had no bearing on the accident.
Fernandes however maintained that AirAsia had the required permission. "What happened was purely an administrative error," he said in an e-mail. "The process has become clear now."
AirAsia has said it is cooperating fully with the ministry's investigations. That investigation would be completed by Friday evening, the transport ministry said on Wednesday.
Indonesia has also reassigned some airport and air traffic control officials who allowed the flight to take off and tightened rules on pre-flight briefing procedures.
Indonesia is one of the world's fastest growing aviation markets and its carriers, such as Lion Air and Garuda Indonesia, are among the top customers for plane makers Airbus and Boeing.
But its safety record is patchy. The European Commission banned all Indonesia-based airlines from flying to the European Union in 2007 following a series of accidents. Exemptions to that ban have since been granted to some carriers, including Garuda and AirAsia.