Indonesian officials say they are sending teams to investigate reports of smoke on an island in the area where AirAsia flight QZ8501 has gone missing.
The multinational search for the plane has entered a third day, with the operation area now widened to cover 13 zones over land and sea.
The Airbus A320-200, carrying 162 people from Surabaya in Indonesia to Singapore, disappeared on Sunday.
The pilot’s last contact was a request to divert around bad weather.
FAQS about AirAsia missing fligh
Indonesian officials say air traffic control had approved one request, to veer left, then gave clearance to a second request for permission to climb two to three minutes later.
No reply was received and the plane then disappeared from radar. No trace has yet been found.
Countries around the region as well as the US, France and Australia have joined the search over the Java sea.
On Tuesday, the head of Indonesia’s search and rescue officials in Banka Belitung province told the BBC they were deploying teams to investigate reports of “billowing smoke” on Long Island, just south of Belitung island, inside the search zone.
Andriandi said the smoke was spotted on Monday by a Chinese television crew, about 29 miles from Manggar in East Belitung.
“There is a possibility that it might be from the missing AirAsia plane but we are still doing further verification,” he said.
Experts have cautioned the smoke could be unrelated to the plane. Reports of a possible oil slick spotted in the seas off Belitung island on Monday turned out to be reefs just below the surface.
Bambang Soelistyo, the head of Indonesia’s search-and-rescue agency, also said on Tuesday that officials would be speaking to two fishermen who had reported hearing a loud bang on Sunday.
But he said no signal had been detected from the plane yet. On Monday, he had said he suspected the aircraft was at the bottom of the sea.
US destroyer en route
On board the plane were 137 adult passengers, 17 children and one infant, along with two pilots and five crew.
Most were Indonesian but the passengers included one UK national, a Malaysian, a Singaporean and three South Koreans.
Pilot Capt Iriyanto had more than 20,500 flight hours, almost 7,000 of them with AirAsia. The co-pilot was French national Remi Emmanuel Plesel.
At least 30 ships, 15 aircraft and seven helicopters joined the operation when it resumed at 06:00 local time, said Indonesian officials, with the search now covering 13 different areas across land and sea.
The multinational operation, led by Indonesia, has been joined by Malaysia, Singapore and Australia, with other offers of help from South Korea, Thailand, China and France. The US destroyer USS Sampson is on its way to the zone.
The BBC’s Alice Budisatrijo at Surabaya’s Juanda airport says those offers come as welcome news to the relatives, who understand the limited technical capabilities of the Indonesian authorities to locate and retrieve the plane, especially if it is underwater.
‘Then no reply’
The plane had left Surabaya at 05:35 Jakarta time and had been due to arrive in Singapore two hours later.
Wisnu Darjono, AirNav safety director, said Capt Iriyanto requested permission to bank left at 06:12 to avoid a storm. The request was immediately granted and the plane changed course.
According to state navigation operator AirNav Indonesia, the pilot then asked to take the plane from 32,000ft (9,800m) to 38,000ft but did not explain why he wanted to do so.
Indonesian air traffic control staff told the pilot he could take the plane to 34,000ft but no higher because another AirAsia airliner was flying at 38,000ft.
“It took us around two to three minutes to communicate with Singapore,” Mr Darjono said. “But when we informed the pilot of the approval at 06:14, we received no reply.”
The plane was officially declared missing at 07:55.
It is unclear what happened next but one report suggests the plane may have tried to climb through the storm.
Former pilots say a climb could have led to reduced stability and possibly a fatal stall, as cross winds and down draughts battered the plane.
The AirAsia plane was delivered in 2008, has flown 13,600 times, completing 23,000 hours, and underwent its last maintenance in November.
AirAsia previously had an excellent safety record and there were no fatal accidents involving its aircraft.