Aircraft and ships resumed searching at daybreak Monday over Indonesian waters near the Equator for an AirAsia jet that disappeared Sunday with 162 people on board in airspace possibly thick with storm clouds, strong winds and lightning, officials said.

"Based on the coordinates given to us and evaluation that the estimated crash position is in the sea, the hypothesis is the plane is at the bottom of the sea," said Bambang Soelistyo, Indonesia's National Search and Rescue Agency chief on Monday.

First Admiral Sigit Setiayana, at the Naval Aviation Center commander at the Surabaya air force base in Indonesia, said the search for AirAsia Flight 8501 had expanded on Monday with 12 navy ships, five planes, three helicopters and a number of warships participating, along with ships and planes from Singapore and Malaysia. The Australian Air Force also sent a search plane.

Several hours after the search resumed, Jakarta's Air Force base commander Rear Marshal Dwi Putranto said he was informed Monday that an Australian Orion aircraft had detected suspicious objects near Nangka island, about 100 miles southwest of Pangkalan Bun, near central Kalimantan, or 700 miles from the location where the plane lost contact.

"However, we cannot be sure whether it is part of the missing AirAsia plane," Putranto says, "We are now moving in that direction, which is in cloudy conditions."

Air Force spokesman Rear Marshal Hadi Tjahnanto told MetroTV that an Indonesian helicopter spotted two oily spots in the Java Sea east of Belitung island. Unlike the Australian discovery, the oily spots were within the search area, which stretches 37 miles around the point where air-traffic controllers lost contact with the plane.

The search had been mostly suspended overnight, said Achmad Toha of Indonesia's search and rescue agency.

Malaysia-based low-cost carrier AirAsia, which has a strong presence in most of Southeast Asia and recently in India, has a good safety record and had never lost a plane before. Flight 8501 was operated by AirAsia Indonesia, a subsidiary that is 49 percent owned by AirAsia Malaysia.

Flight 8501 is the third major aviation incident involving Malaysia this year. In March, Malaysia Airlines Flight 370 disappeared with 239 people en route from Kuala Lumpur to Beijing, and has not been found. In July, a jet from the same airline was shot down over Ukraine amid the conflict there, killing all 298 people aboard.

In the latest incident, the plane took off Sunday morning from Surabaya, Indonesia's second-largest city, and was about halfway to its destination, Singapore, when it vanished from radar.

The last communication between the pilot and air traffic control was at 6:13 a.m. local time, when the pilot "asked to avoid clouds by turning left and going higher to 34,000 feet." The plane was last seen on radar at 6:16 a.m., and a minute later was no longer there, Djoko Murjatmodjo, Indonesia's acting director general of transportation, told reporters.

Officials did not publicly speculate about what may have happened. Industry analysts said prospects were not promising. "It is more than likely that the plane has gone down, seeing that with a relatively short flight of 2.5 hours, four hours endurance is the likely amount of fuel it had on board," Ron Bartsch, a Sydney-based aviation consultant, told Al Jazeera.

Hours after the plane disappeared, shocked family members huddled and awaited any news at the Surabaya airport, where the Airbus A320 had taken off.

"I hope for a miracle, and may God save them all," said a man at the airport. He told Al Jazeera he had two friends on board.

AirAsia Group CEO Tony Fernandes flew to Surabaya and said at a news conference that that the focus should be on the search and the families.

"We have no idea at the moment what went wrong," said Fernandes, a Malaysian businessman who founded the regional budget airline in 2001. "Let's not speculate at the moment."

Airbus, the French manufacturer that built the missing plane, issued a statement saying that it had been delivered to AirAsia in October 2008, and that it had accumulated about 23,000 flight hours in some 13,600 flights. AirAsia said the aircraft had last undergone scheduled maintenance on Nov. 16.

The Airbus A320 is a workhorse of modern aviation. Similar to the Boeing 737, it is used to connect cities anywhere from one to five hours apart. There are currently 3,606 A320s in operation worldwide, according to Airbus. The A320 family of jets has a very good safety record, with just 0.14 fatal accidents per million takeoffs, according to a study published by Boeing in August.

AirAsia is a major purchaser of Airbus planes. In 2011, the airline bought 200 A320neo planes, which the manufacturer said in a statement was "the largest order ever placed for the A320 Family and makes AirAsia the biggest airline customer for the Airbus single aisle product line worldwide."

Indonesia and Singapore launched a search and rescue operation for Flight 8501 near Belitung island in the Java Sea, the area where the jetliner lost contact with ground traffic control about 42 minutes after taking off from Surabaya.

Murjatmodjo, the Indonesian transport director, said there had been no distress signal from the cockpit of the twin-engine, single-aisle plane.

"We hope we can find the location of the plane as soon as possible, and we hope that God will give us guidance to find it," he said.

Ramin Pourteymour, a former airline captain and chairman of consultancy Aviation Experts LLC, said it was too early to say what happened.

"Weather systems or pilot experience and training could be factors," he told Al Jazeera by email. "But we cannot know until the investigation is complete and facts are found."

The plane had an Indonesian captain and a French co-pilot, five cabin crew and 155 passengers, including 16 children and one infant, AirAsia Indonesia said. Among the passengers were three South Koreans, a Malaysian, a British national and his 2-year-old Singaporean daughter. The rest were Indonesians.

AirAsia said the captain has a total of 6,100 flying hours, but Fernandes later put it at over 20,000. The airline said the first officer has 2,275 flying hours.

Transport Minister Ignasius Jonan told reporters in Surabaya that search and rescue efforts now involve the Indonesian army and the national Search and Rescue Agency, as well as Singapore and Malaysia.

The Search and Rescue Agency's operation chief, Maj. Gen. Tatang Zaenudin, said 200 rescuers had been deployed to the east side of Belitung island.

AirAsia, which has dominated cheap travel in the region for years, flies short routes of just a few hours, connecting large cities of Southeast Asia. Recently it has tried to expand into long-distance flying through its sister airline AirAsia X.

Flight 8501 disappeared while it was at its cruising altitude, which is usually the safest part of a trip. Just 10 percent of fatal crashes from 2004 through 2013 occurred while a plane was in that stage of flight, according to the August Boeing safety report.

Al Jazeera and The Associated Press