TAIPEI (AFP) - Taiwan grounded all military aircraft for training and exercises after a pilot was killed and another went missing on Monday (March 22) when their fighter jets had a suspected mid-air collision.

The air force made the announcement after two single-seater F-5E aircraft disappeared from radar at around 3pm local time some 2.6km off the coast of southern Pingtung county.

They were among four F-5Es that took off about 30 minutes earlier for a routine training mission, and the incident occurred when they were changing formation at an altitude of some 14,000 feet, air force Chief of Staff Huang Chih-wei said.

An initial probe showed that a crash between the two jets was the suspected cause and that "mechanical and weather factors" were not involved, he added.

One of the pilots was found unconscious in the sea but could not be resuscitated and was pronounced dead at the hospital. The other pilot is still missing.

It was the third fatal crash in less than six months in Taiwan.

"The air force has temporarily grounded for all its aircraft for (safety) reviews... We've suspended training and exercises, although 'combat readiness' missions will be carried out normally," Major-General Huang said.

"The defence ministry is making every effort in the hope of rescuing the missing pilot within the golden 72 hours" of rescue time, he told reporters.

The National Rescue Command Centre said two helicopters and six coastguard ships had joined the search.

Police confirmed that they found a seat with a parachute attached on a local highway.

Taiwan's ageing fighter fleet suffered a string of fatal accidents in recent years, as the island's air force is kept under constant pressure by China.

Beijing views Taiwan as a breakaway province to be reunified - by force if necessary.

Under President Xi Jinping, China became markedly more hostile towards Taiwan, and last year, incursions by Beijing's fighter jets reached record highs.

The incursions force outgunned Taiwan to regularly scramble its jets and keep pilots trained on a round-the-clock war footing that takes its toll on ageing aircraft and those flying them.

In October 2020, an F-5E pilot was killed when his plane crashed off the island's eastern coast.

A month later, Taiwan temporarily grounded all F-16 fighters for safety checks after one went missing during a training exercise.

The F-5E is an older generation fighter with a design that dates back to the 1960s.

There were nine incidents involving F-5E jets in the past two decades, including Monday's crash, that left 10 pilots dead and three missing.

Last year, Chinese military jets made a record 380 incursions into Taiwan air defence identification zone, with some analysts warning that tensions between the two sides were at their highest since the mid-1990s.

On Monday, Taiwan's defence ministry said it scrambled combat air patrol aircraft and broadcast warnings to leave when two Chinese J-10 fighters entered its south-west air defence identification zone.