Large areas of southern China were hit by the worst storms and floods in decades, the government said on Tuesday, as warnings emerged that the Yellow River in the north could also wreak havoc for millions.

The prosperous Pearl River Delta was being ravaged by rising waters, with parts of the major urban centres of Guangzhou and Shenzhen submerged by flooding.

"We must remain clear-headed and not underestimate the serious nature of the current flood and disaster situation," Vice Premier Hui Liangyu said in comments posted on the website of the state flood prevention headquarters.

The entire Pearl River was flooded, while some of its tributaries were experiencing the biggest floods ever recorded, Hui said.

The civil affairs ministry said the death toll in nine southern provinces and regions had reached 63 as of Tuesday, with 13 missing since torrential rains began pummelling the area on June 7.

More than 1.66 million people have been evacuated in the hardest-hit areas, with large swathes of farmland submerged and economic losses totalling 14.5 billion yuan (2.1 billion dollars), the ministry said.

Hui also ordered the immediate evacuation of people in danger areas and the strengthening of river dikes and reservoirs as water levels on over 40 rivers nationwide exceeded warning levels.

"We have to limit the loss of life and property to the lowest extent possible," Hui said. "We cannot underestimate the arduous nature of fighting the flooding and warding off disaster."

According to the flood headquarters, waters exceeded warning levels by 6.8 metres (22 feet) on the Xijiang river in Guangxi's Wuzhou city, where three rivers meet before flowing down into the Pearl river delta.

Rains were expected to continue in the region this week.

In the north, the government urged the strengthening of dikes and reservoirs along the Yellow River, which is known as the "cradle of Chinese civilisation" and is home to millions of urban dwellers and farmers.

"National flood prevention and relief efforts are entering a crucial phase," the flood headquarters said in a statement.

"According to the water and meteorological departments, we could be seeing torrential rains and flooding along the Yellow River."

Meanwhile, Prime Minister Wen Jiabao ordered stepped-up efforts to fight rain-induced landslides in Sichuan province, where an 8.0 magnitude earthquake in mid-May left 87,000 people dead or missing and millions homeless.

"As aftershocks continue to hit and as rains markedly increase at the start of the rainy season, we must pay close attention to (landslides) that may occur," Wen said.

Up to 70,000 people at the quake epicentre in Wenchuan county have been evacuated in recent days from mountainous areas where rain-induced rock and mudslides could occur, state press reports said.