The Boeing 737-500, en route to Pontianak in West Kalimantan, disappeared from radar screens after taking off just after 2.30 pm (0730 GMT) - 30 minutes after the scheduled time because of heavy rain.
A Sriwijaya Air plane has crashed into the sea minutes after taking off from Indonesia's capital Jakarta on a domestic flight with 62 people on board.
Flight tracking data showed the Sriwijaya Air Boeing 737-500 plunged into a steep dive about four minutes after it left Soekarno-Hatta international airport on Saturday.
Sixty-two passengers and crew were on board, including 10 children, the nation's transport minister, Budi Karya Sumadi, told reporters.
The suspected crash site is near tourist islands just off the coast of Indonesia's sprawling capital.
Sriwijaya Air flight SJ182 was bound for Pontianak on Indonesia's section of Borneo island, about 90 minutes flying time over the Java Sea.
Distraught relatives waited nervously for news at the city's airport.
"I have four family members on the flight – my wife and three children," Yaman Zai said as he sobbed.
"(My wife) sent me a picture of the baby today...How could my heart not be torn into pieces?"
The plane took off on Saturday afternoon and a search and rescue operation began with no official results available on Saturday night.
"We deployed our team, boats and sea riders to the location suspected to be where it went down after losing contact," Bambang Suryo Aji, a senior official at the search-and-rescue agency, told reporters after nightfall.
Data from FlightRadar24 said the plane reached an altitude of nearly 3,350 metres (11,000 feet) before dropping suddenly to 250 feet. It then lost contact with air traffic control.
"Sriwijaya Air flight #SJ182 lost more than 10,000 feet of altitude in less than one minute, about 4 minutes after departure from Jakarta," the tracking agency said on its official Twitter account.
Broadcaster Kompas TV quoted local fishermen as saying they had found debris near islands just off the coast of the capital Jakarta, but it could not be immediately confirmed as having belonged to the missing jet.
Authorities and the airline gave no immediate indication as to why the plane suddenly went down.
But transport minister Sumadi said the jet appeared to deviate from its intended course just before it disappeared from radar.
Among the other passengers was Agus Minari and her husband who were on their way back to Pontianak after visiting her son and attending a funeral in Java, according to her cousin Deni Triady.
"The family is deeply shocked," Triady added.
Russian President Vladimir Putin issued a statement offering his "sincere condolences" over the incident.
The budget airline, which has about 19 Boeing jets that fly to destinations in Indonesia and Southeast Asia, said only that it was investigating the loss of contact.
We speak to aircraft accident investigator Fahad Masood about possible causes for Sriwijaya Air flight crashing into the sea after taking off from Jakarta pic.twitter.com/CUjNykv3W8— TRT World Now (@TRTWorldNow) January 9, 2021
Patchy safety record
In October 2018, 189 people were killed when a Lion Air Boeing 737 MAX jet slammed into the Java Sea about 12 minutes after take-off from Jakarta on a routine one-hour flight.
That crash – and a subsequent fatal flight in Ethiopia – saw Boeing hit with $2.5 billion in fines over claims it defrauded regulators overseeing the 737 MAX model, which was grounded worldwide following the two deadly crashes.
The Boeing jet thought to have crashed Saturday is not a MAX model and was 26 years old, according to authorities.
"We are aware of media reports from Jakarta, and are closely monitoring the situation," the US-based plane maker said in a statement.
"We are working to gather more information."
Indonesia's aviation sector has long suffered from a reputation for poor safety, and its airlines were once banned from entering US and European airspace.
In 2014, an AirAsia plane crashed with the loss of 162 lives.
Domestic investigators' final report on the AirAsia crash showed a chronically faulty component in a rudder control system, poor maintenance and the pilots' inadequate response were major factors in what was supposed to be a routine flight from the Indonesian city of Surabaya to Singapore.
A year later, in 2015, more than 140 people, including people on the ground, were killed when a military plane crashed shortly after takeoff in Medan on Sumatra island.
Between 2007 and 2016, the US Federal Aviation Administration lowered its Indonesia safety evaluation to Category 2, meaning its regulatory system was inadequate.
Indonesian officials say they have worked hard to bring safety up to international standards.
Dear sister Retno, my heartfelt condolences for the airplane crash near Jakarta. May Allah’s mercy be upon those who lost their lives in this terrible tragedy. Sharing brotherly Indonesian people’s grief.🇹🇷🇮🇩 @Menlu_RI— Mevlüt Çavuşoğlu (@MevlutCavusoglu) January 9, 2021
Turkey extends condolences
Turkey has extended condolences to Indonesia over the plane crash.
"We have learned with great sorrow that a passenger airplane flying from Jakarta to the city of Pontianak in Indonesia crashed shortly after takeoff today, resulting in the loss of lives of more than 60 people," the Turkish Foreign Ministry said in a statement.
"We share the grief of friendly and brotherly people of Indonesia. We wish the mercy of Allah upon those who lost their lives in the tragic accident and extend our heartfelt condolences to their bereaved loved ones," the statement added.
Foreign Minister Mevlut Cavusoglu personally condoled with Indonesian counterpart Retno Marsudi in a phone talk.