"All the Chinese coast guard went back to China yesterday, thus, although they haven't officially made any announcement, we consider it over," Hsieh Ching-chin, deputy director general of Taiwan's coast guard, told AFP.

Beijing held its biggest maritime drills in years, stretching from near the southern islands of Japan to the South China Sea, Taiwanese authorities said this week.

About 90 Chinese warships and coast guard vessels were involved in the exercises that include simulating attacks on foreign ships and practising blockading sea routes, a Taiwan security official said Wednesday.

There was no announcement by Beijing's army or Chinese state media about increased military activity in the East China Sea, Taiwan Strait, South China Sea or Western Pacific Ocean.

"The nine ships went back to Chinse ports last night in two groups," Hsieh said of vessels that had been in waters to the southeast and southwest of Taiwan.

A defence ministry spokeswoman said Friday that Chinese warships and coast guard vessels had been detected returning to China.

Taiwan's military on Thursday closed emergency response centres that were set up in response to the huge mobilisation of Chinese ships.