The single-seater F-16V jet was being piloted by Republic of China Air Force (ROCAF) Capt. Chen Yi when the aircraft disappeared from radars off Dongshi Township in Chiayi at around 3:30 p.m. local time, ROCAF Maj. Gen. Liu Hui-chien told a press briefing.

Chen’s F-16V—tail code 6650—was unarmed while taking part in a ground firing exercise at the Shuixi shooting range when the American-made jet was seen “crashing into the sea at a steep angle,” said Liu. Witnesses saw no parachute, he said.

Liu said the rescue mission would continue into the night. Taiwan President Tsai Ing-wen ordered the air force’s F-16Vs to be grounded for inspection, he said.

Liu told the emergency press conference that weather conditions at the time of the training exercise were within permitted standards: cloudless, with visibility of up to 7 nautical miles.

Chen, 28, had 321.5 flight hours, including 60.5 in F-16Vs, he said. Defense contractor Lockheed Martin has been upgrading Taiwan’s F-16A/B models since 2016, with about half the fleet yet to be retrofitted. Taiwan is also expecting delivery of 66 new F-16Vs purchased from the United States during the Donald Trump administration.

The aircraft piloted by Chen was manufactured on July 24, 1998, and had 3,415.5 flight hours, said Liu. It was last inspected on December 28, 2021, and had no record of incidents.

Tuesday’s crash came less than three months after Tsai commissioned her country’s first F-16V squadron at Chiayi Air Base on November 18, 2021. She praised the event as a testimony to Taipei’s defense partnership with Washington. The U.S. is the only country in the world that regularly supplies the island with defensive arms.

This is Taiwan’s second military incident involving an F-16 since November 17, 2020, when one piloted by ROCAF Maj. Gen. Chiang Cheng-chih, 44, crashed into the sea shortly after takeoff from Hualien Air Base in east Taiwan. Neither his body nor the aircraft was recovered.

Taiwan’s air force pilots and fighter aircraft have become precious commodities in recent years amid a surge in Chinese air operations in the skies around the island, which Beijing claims as part of its historical territory.

The routine military aircraft sorties from the mainland are met by Taiwanese interceptors from bases including in Chiayi. Meeting the pressure is taking a toll on Taiwan’s outnumbered air force and its personnel.

UPDATE 01/11/22 7:26 a.m. ET: This article was updated to include additional information.