A tropical storm in China has left 21 people dead and 13 missing, reports said Thursday, after it lashed Taiwan with typhoon-grade winds and rain.

Super Typhoon Nepartak brought chaos to Taiwan last week, forcing more than 15,000 people to flee their homes as part of the island saw its strongest winds in over a century.

It had weakened into a tropical storm by the time it made landfall in Fujian province on Saturday, but still wreaked havoc, with pictures showing cars upended, buildings ripped apart and towns left wallowing in a thick sludge of brown mud.

By Thursday more than half a million had been forced to evacuate and some 8,300 homes destroyed, the official Xinhua news agency said.

21 people had been killed and 13 remained missing, it reported, while saying that direct economic losses had reached 7 billion yuan ($1 billion).

Six cities were flooded, with precipitation in two counties reaching record highs, the official Xinhua news agency said.

Nepartak killed three people in Taiwan and injured more than 300, according to the island's central emergency operation centre.

Flooding is common during the summer monsoon season in southern China, but rainfall has been particularly heavy this year and many areas have been lashed by torrential rains this week.