Since Friday, more than 270,000 people across Ghuizhou province have been affected by floods [AP]

Flash floods triggered by heavy rains have killed at least 21 people and left 31 others missing while wreaking havoc in southwest China, according to state TV.

About 45,000 residents in Guizhou province's Wangmo County have been evacuated since flood waters started inundating the area on Monday, the Xinhua news agency, citing local officials, said on Wednesday.

Another 3,000 people remained stranded across Wangmo County, according to the reports.

The deluge has toppled 300 houses and a left 2,400 submerged, while  5,500 hectares of farmland were under water.

The country's army has been drafted in to clear debris and help with rescue efforts and evacuations.

The flooding also disrupted power and water supplies and telecommunication services in several towns in Wangmo County, which has a population of 8m.

It said the floods destroyed roads and bridges and washed away more than 500 vehicles.

The floods have prevented about 6,000 students from attending school on Tuesday, Yan Tie, the county's education chief, told Xinhua.

The provincial civil affairs bureau said the floods had hit 11 cities and counties in Guizhou province since June 3, affecting 270,000, according to Xinhua.

More rain was forecast for Wednesday in most parts of the province.

Source: Agencies