JAKARTA, Indonesia — Indonesian officials on Monday expanded the search area for a missing AirAsia jetliner and said they suspect the plane is at “the bottom of the sea.”

Officials said no signals had been detected from the aircraft’s emergency locator transmitters, or ELTs, and as teams resumed the search for the plane after pausing overnight, the search area was widened from around Bangka island south of Singapore to include waters farther north, in addition to a part of the island of Borneo.

Indonesia Air Asia Flight 8501 with 162 people on board vanished in a thicket of storm clouds en route to Singapore from the Indonesian city of Surabaya on Sunday morning. It lost contact with air-traffic control less than an hour after takeoff after requesting to climb to a higher altitude to avoid bad weather, officials said.

“Based on the location coordinates given to us, our preliminary assessment is that the plane is at the bottom of the sea,” Bambang Soelistyo, head of Indonesia’s search-and-rescue efforts, told reporters in Jakarta. “But we will develop this further.”

Tatang Kurniadi, chief of Indonesia’s national transportation safety committee, said the lack of a detected signal could be because the ELTs are broken, mountains are blocking signals or the plane isn’t on land.

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The disappearance of Flight 8501 is the AirAsia group’s first significant incident. In recent years, Indonesia’s aviation authorities have come under criticism and enhanced scrutiny by both U.S. and European safety officials, and international air-safety experts have expressed concerns that soaring growth in air travel in the broader region could erode safety margins.

Those on board Sunday’s AirAsia flight included 155 Indonesians, three South Koreans, one U.K. citizen, one Malaysian, one Singaporean and one French citizen, airline officials said. Seventeen of the passengers were children. The plane was carrying two pilots and five other crew members.

AirAsia said the missing Airbus underwent its last scheduled maintenance on Nov. 16. Airbus said the Indonesia AirAsia plane was delivered in October 2008 and had accumulated about 23,000 flying hours in 13,600 flights and had CFM56-5B engines.

An expanded version of this report appears on WSJ.com