(CNN) -- The missing AirAsia jet probably crashed into the sea, Indonesia's top rescue official said Monday, citing radar data from the plane's last contact.
"Our early conjecture is that the plane is in the bottom of the sea," Bambang Sulistyo, head of Indonesia's national search and rescue agency, told reporters, saying the view was based on the plane's flight track and last known coordinates.
But searchers still don't know exactly where the aircraft is, he said, and may need help from other countries for an underwater search.
The search for AirAsia Flight QZ8501 resumed on Monday, a day after the commercial jet disappeared in Indonesian airspace with 162 people aboard.
Ships, planes and helicopters are looking for the missing aircraft, according to Indonesian authorities, who are leading the search and rescue operations.
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It's unclear if weather played a role in the aircraft's disappearance, but rescuers say it could be a factor that influences how quickly they find the plane.
Large waves and clouds hampered the search for the plane on Sunday, the agency said. By Monday morning, weather in the area appeared to be clearing up, CNN International meteorologist Tom Sater said.
Authorities say they're combing a "very broad search area."
AirAsia says air traffic controllers lost contact with the aircraft at 7:24 a.m. Sunday Singapore time (6:24 a.m. in Indonesia).
The plane, flying from the Indonesian city of Surabaya to Singapore, went missing as it flew over the Java Sea between the islands of Belitung and Borneo -- a heavily traveled shipping channel with shallow waters -- Indonesian authorities said.
Before the plane, an Airbus A320-200, lost contact with air traffic controllers, one of the pilots asked to change course and fly at a higher altitude because of bad weather, officials said. Heavy thunderstorms were reported in the area at the time.
Air traffic control approved the pilot's request to turn left but denied permission for the plane to climb to 38,000 feet from 32,000 feet, Djoko Murjatmodjo, an aviation official at the Indonesian Transport Ministry told the national newspaper Kompas.
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The increased altitude request was denied because there was another plane flying at that height, he said.
In addition to Indonesia's teams, several other countries have joined the hunt for the missing plane.
A C-130 plane from Singapore has been participating in the search, and the country's military says it's sending two more ships to the search area. Malaysia's transportation minister said his country has deployed three vessels and three aircraft to assist in the search. And the Royal Australian Air Force said Monday that it was deploying a patrol plane to help.
The U.S. Navy Seventh Fleet said it stands ready to assist the search efforts but so far hasn't been asked to help.
Indonesia has reached out to the United Kingdom, France and the United States for help with sonar technology that may be needed for an underwater search, Sulistyo told reporters Monday.
After hours of waiting in anguish for any word about the passengers aboard the missing plane, several dozen of their family members met with airport and airline officials in a closed-door briefing Monday at the airport in Surabaya.
As they waited for news, some relatives took cell phone pictures of a flight manifest posted on a wall. The black-and-white papers showed every passenger's name and seat number, but not their fate.
Others simply sat and dabbed tears from their eyes.
Oei Endang Sulsilowati and her daughter were looking for information about her brother, his wife and their two children.
"We don't know what to do," Sulsilowati said. "We are just waiting for news."
"Our concern right now is for the relatives and the next of kin," AirAsia CEO Tony Fernandes said during a news conference in Surabaya.
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Fernandes confirmed that storm clouds caused the pilot to ask for a change in flight plan, but added, "We don't want to speculate whether weather was a factor. We really don't know." Once the aircraft is found, there will be a proper investigation, he said.
Of the people on board the passenger jet, 155 are Indonesian, three are South Korean, one is British, one is French, one is Malaysian and one is Singaporean, the airline said.
Eighteen children, including one infant, are among the passengers, the carrier said. Seven of the people on board are crew members.