JAKARTA - Dozens of planes and ships searching Indonesian waters for a missing AirAsia plane focused Monday on a patch of oil for possible clues, as a senior official warned the aircraft was likely at the bottom of the sea.
Australia, Malaysia and Singapore joined the Indonesia-led search, with China stating it was also sending help as anguished relatives awaited news of their loved ones more than a day after Flight QZ8501 disappeared over the Java Sea with 162 people on board.
"Papa come home, I still need Papa," Angela, the daughter of the Indonesian pilot Irianto, begged in an emotional appeal on local social media.
The Airbus A320-200 lost contact en route from Surabaya in Indonesia's east Java to Singapore on Sunday after the crew requested a change of flight plan due to stormy weather, in the third crisis for a Malaysian carrier this year.
Indonesian Air Force spokesman Hadi Tjahjanto told AFP the search was now concentrated on an oil patch spotted off Belitung island, across from Kalimantan on Borneo island.
"We are making sure whether it was avtur (aviation fuel) from the AirAsia plane or from a vessel because that location is a shipping line," he said.
As the second day's search ended at dusk, National Search and Rescue Agency chief Bambang Soelistyo said an Indonesian corvette was on its way to collect an oil sample, with an announcement expected Tuesday.
Soelistyo earlier said it was likely the plane was at the "bottom of the sea".
The hypothesis is "based on the coordinates given to us and evaluation that the estimated crash position is in the sea", he told journalists.
Ships and aircraft were searching an area where the sea is 40-50 metres (130-160 feet) deep, he said, adding that Indonesia was coordinating with other countries to borrow any equipment needed to scour the seabed.
The United States confirmed Monday that Jakarta had asked for its assistance in the search.
"We are reviewing that request to find out how best we can meet Indonesia's request for assistance," said a State Department spokesman, adding the process could take "a little bit of time" and without detailing what kind of aid - military or otherwise - the US might provide.
China, which had 152 citizens on MH370, said in a statement Monday that it would send a navy frigate and a military jet to join in the search.
Distraught relatives in Surabaya were desperately hoping for news of loved ones as the international search expanded.
Intan, 28, said Indonesia needed overseas help to find the plane which was carrying her brother and his family and friends.
"My hope is Indonesia seeks as much help as possible from other countries. Don't claim 'We have sophisticated technology', just ask other countries because they are better equipped," she told AFP, as Jakarta welcomed offers of help from its neighbours.
In the French Caribbean island of Martinique, the mother of co-pilot Remi Emmanuel Plesel told AFP of her heartbreak and "the bad feeling" she had when the phone rang in the middle of the night.
"He wanted to be a pilot ever since he was a child," Rolande Plesel said.
While the international operation has drawn comparisons with the ongoing search for Malaysia Airlines MH370, Australian Prime Minister Tony Abbot said it did not appear to be a great mystery.
"It doesn't appear that there's any particular mystery here," Abbott told Sydney radio station 2GB.
"It's an aircraft that was flying a regular route on a regular schedule, it struck what appears to have been horrific weather, and it's down. But this is not a mystery like the MH370 disappearance and it's not an atrocity like the MH17 shooting down."
One Indonesian family of 10 had a miraculous escape when they arrived too late to catch Flight QZ8501.
"Maybe it is all God's plan that my family and I were not on the flight. It was a blessing in disguise," said Christianawati, 36.
AirAsia said 155 of those on board were Indonesian, with three South Koreans and one person each from Singapore, Malaysia, Britain and France. The Frenchman was the co-pilot.
Air traffic controllers lost contact with the twin-engine aircraft around an hour after it left Surabaya's Juanda international airport at about 5:35 am Sunday (2235 GMT Saturday).
Shortly before the plane disappeared, the pilot asked to ascend by 6,000 feet to 38,000 feet to avoid heavy clouds but his request was turned down due to another flight above him.
The missing plane was operated by AirAsia Indonesia, a unit of Malaysian-based AirAsia which dominates Southeast Asia's booming low-cost airline market.
Indonesia, a vast archipelago with poor roads and railways, has seen explosive growth in low-cost air travel over recent years.
But the air industry has been blighted by low safety standards in an area that also experiences extreme weather.
AirAsia, which has never suffered a fatal accident, said the missing jet last underwent maintenance on November 16.
Its shares slumped 12 per cent at the open but recovered slightly to close 8.50 per cent lower in Kuala Lumpur.
The plane's disappearance comes at the end of a disastrous year for Malaysian aviation.
Malaysia Airlines Flight MH370 disappeared while flying from Kuala Lumpur to Beijing in March with 239 passengers and crew, and in July flight MH17 was shot down over troubled Ukraine killing all 298 on board.