Taiwan has closed a busy motorway to let fighter jets use it as an emergency runway and practice refuelling.
Some sections of the motorway are designated emergency runways
The drill - the first of its kind in 26 years - comes as China conducts war games in the Taiwan Straits.
The exercise in southern Tainan County assumes a battle scenario where China has destroyed the island's air strips with short-range missiles and bombers.
China sees Taiwan as a renegade province, to be allied to the mainland by force if necessary.
The BBC's Chris Hogg says Taiwan's military exercise is about practising, but also about posturing, as Taipei wants to show it can resist the military threat,
'Chinese Glory' drill
An eight-kilometre (five mile) section of the motorway will remain closed from 0300 local time (1900GMT) for six hours to allow two French-made Mirage jets practice landing, refuelling and taking off.
Hundreds of makeshift concrete blocks separating traffic lanes have already been removed, turning several sections of the motorway into designated emergency runways.
The exercise is part of Taiwan's series of annual war games, called the Hankuang, or Chinese Glory, Taiwan's Defence Ministry spokesman Huang Shey-sheng told reporters.
"We will practice using the motorway as a runway at the time of a war," the spokesman added.
Taiwan's navy also plans to stage an exercise on Wednesday, which will involve several vessels and anti-submarine aircraft, our correspondent says.
But he says officials have urged the public not to be concerned by their manoeuvres and those of their rivals, the Chinese.
Such exercises are often held at this time of year as both sides take advantage of the good weather, our correspondent adds.
China's military drill - reportedly involving some 18,000 troops on the island of Dongshan - simulates an invasion of Taiwan.