Monday’s crash was the third such incident in the past half of the year, at a time when the island’s armed forces must intercept Chinese planes almost daily.
The two F-5E jets disappeared from radar around 3 p.m. (0700 GMT) about 2.6 km (1.6 miles) off the coast of rural southern Pingtung County, the National Rescue Command Center said.
He added that the fighters, each with a pilot on board, crashed into the sea off the island’s southeast coast after apparently crashing into the air during a training mission.
One of the pilots was found unconscious at sea but could not be resuscitated and was pronounced dead in hospital.
Rescuers were still looking for the remaining pilot.
Taiwan’s Defense Ministry said it was working on a statement and provided no further immediate comment. The official Central News Agency said the Air Force has now grounded the F-5 fleet operating out of Chihhang Air Base.
Another F-5 crashed in October, killing the pilot. The following month, a much more modern F-16 crashed off the east coast of Taiwan, the pilot of which also died.
In January last year, Taiwan’s top military official was among eight people killed when a helicopter carrying them to visit soldiers crashed in a mountainous area near the capital Taipei.
While the Taiwan Air Force is well trained and equipped, mostly with equipment made in the United States, it is eclipsed by that of China.
Beijing regards the democratic island as its own territory and has never renounced the use of force to bring it under Chinese control.
Under President Xi Jinping, China has become significantly more hostile to Taiwan and last year Chinese planes made a record 380 forays into its defense zone, with some analysts warning that tensions between the two sides are at their core. highest since the mid-1990s.
The force of the incursions has surpassed Taiwan in regularly jamming its own planes and keeping pilots on a war footing around the clock, taking a toll on aging planes and those who fly them.
The American-built F-5E is an older generation fighter with a design that dates back to the 1960s.
It first entered service in Taiwan in the late 1970s and was mainly withdrawn from frontline operations, although some are still used for training and as reinforcements for the main fleet.