Traces of oil have been spotted in the Java Sea in the area where the missing AirAsia plane is thought to have gone down.

But objects seen by rescue teams there are not now thought to be connected to it.

It is also reported air traffic control refused permission for the jet, which had 162 people on board, to change course to avoid a storm.

Indonesian officials said the search team had made the discovery while searching for the jet which stopped communicating with air traffic control over the Java Sea in the early hours of Sunday morning.

It came after air force spokesman Hadi Tjahjanto said searchers had picked up an emergency locator signal off the south of Borneo island but had been unable to pinpoint it.

Earlier, the chief of Indonesia's search effort said that the missing AirAsia passenger plane "is likely at the bottom of the sea".

Bambang Soelistyo added that an initial investigation into the disappearance of Flight QZ8501 had revealed that the "estimated crash position is in the sea", as more than a dozen ships try to find the aircraft.

The Airbus A320 stopped communicating with air traffic control over the Java Sea in the early hours of Sunday morning. The pilot issued no distress signal.

According to the AFP news agency, he added: "Due to the lack of technology that we have, I have coordinated with our foreign minister so we will borrow from other countries which have offered. They are the UK, France and US."

"It is not easy to look for something underwater...That will not break our spirit to continue searching, no way."

Airline statement

In a statement, the airline said: "AirAsia Indonesia has received confirmation from The National Search and Rescue Agency Republic of Indonesia (BASARNAS) that an international search and rescue mission from Indonesia, Singapore and Malaysia has been mobilized in the search of flight QZ8501. The mission in Surabaya has resumed today at 06.00 AM LT."

"AirAsia Indonesia continue to support these efforts and has been actively cooperating with the search and rescue authorities."

"AirAsia Indonesia's primary focus remains on the families and Sunu Widyatmoko, chief executive officer of AirAsia Indonesia is currently stationed at the family centre in Surabaya. We have been keeping the families updated on the search and rescue efforts as well as provide emotional support. Another group of AirAsia officials are providing the same to the families based in Singapore."

"We will release further information as soon as it becomes available and our thoughts and prayers are with those on board QZ8501," it added.

An emergency call centre has been set up for families seeking information. The number is +62-212-9270-811.

Families of missing travellers have said his comments were "not appropriate at all", especially considering the flight had not been found.

A British businessman and his two-year-old daughter are among the 162 people on board the jet, which was travelling from the Indonesian city of Surabaya to Singapore.

The main focus of the search-and-rescue operation lies near Belitung island, where the plane last made contact.

Five planes, three helicopters, 12 navy ships and several warships have been deployed, officials have confirmed.

A Royal Australian Air Force aircraft has also joined the effort, with Prime Minister Tony Abbott pledging that his country would do "whatever it humanly can to assist".

First Admiral Sigit Setiayana said visibility was good, adding: "God willing, we can find it soon." Several storm clouds were along the route of the flight, and Sunday's search for the Airbus A320 was hampered by heavy rain.

"Worst nightmare"

AirAsia is a low-cost carrier which has been in operation since 2001. It has a good safety record, and none of its planes have gone missing before.

The company's founder, Tony Fernandes, has described the incident as "his worst nightmare".

The experienced captain of the plane, who has amassed more than 20,000 flying hours, had requested to change route because of bad weather.

His 22-year-old daughter has used social media to beg for his safe return, writing: "Papa, come home, I still need you."

A fellow pilot, Rakam Singh, said: "As you climb higher the temperature gets lower...if you hit turbulence you've got more chance of stalling an aircraft if you hit this kind of weather."

He said the chances of carrying out a safe landing after that were low.

This year has been the worst year for aviation accidents in a decade - largely as a result of the MH17 and MH370 disasters. Shares in AirAsia fell by 11.6% at the start of trade in the Malaysian stock market on Monday morning.