BEIJING -- More than 10 million people were under threat from potentially devastating floods in central China Tuesday, as a vast lake which acts as a buffer for the Yangtze River surged above danger levels, officials and reports said.

With more torrential rain from a looming tropical storm forecast for coming days, tens of thousands of local people were racing to shore up thousands of kilometers (miles) of embankments around Dongting Lake, officials said.

There was a possibility the area could be hit by floods as bad as those of 1998, when 4,000 people died, one official warned.

"The lake is above warning marks in a number of places," said the official, from the Hunan Anti-Flood Bureau headquarters in the provincial capital of Changsha.

Asked whether the situation was better than in 1998 -- after which flood defenses were massively beefed up -- he said that could not be known for certain.

"Everything is changing very quickly, it is very difficult to say things are better," said the official, who declined to give his name.

Were the 2,800 square-kilometer (1,070 square-mile) lake to burst through embankments, the devastation could dwarf that so far in a summer which has already seen around 900 people die in flooding throughout the country, AFP reported.

With swollen rivers emptying into the lake, more than 10 million people and 667,000 hectares (1.67 million acres) of farmland were under threat, the ***China Daily ***said.

Authorities around Dongting, China's second-biggest freshwater lake, "are preparing for possibly the worst flood of the year", the paper said.

Around 40,000 officials and laborers had been sent to help shore up defenses, the Hunan Anti-Flood Bureau official said.

Water levels at the traditional danger spot of Chenglingji, where the Yangtze exits the lake, were well above warning marks Tuesday, an official at the local Anti-Flood Bureau said.

At 3:00 P.M. (0700 GMT), the waters were more than a meter and a half (five feet) above flood warning marks, said the official, who gave her name as Chen.

To add to concerns, meteorologists warned Tuesday that tropical storm Vongfong was due to dump yet more rain over Hunan as it heads across the country.

Vongfong hit the southern Province of Guangdong around 8:40 P.M. Monday (1200 GMT) and was gradually moving northeast, weakening as it went, the Central Meteorological Bureau in Beijing said.

It is expected to bring torrential rain to southern Guangdong, Guizhou and Guangxi provinces as well as Hunan.

Vongfong drenched southern China Monday and Tuesday, stranding air and rail passengers but causing no reported casualties.

The far southern island of Hainan was battered Monday, with 113 flights delayed and more than 3,000 passengers stranded, the official ***China New Service ***said.

A smaller number of flights as well as trains and ships were stranded or forced to stay put in Guangdong, local newspaper reports said.

This year's flood season started early with a series of devastating flash floods in June, prompting official warnings that the 1998 toll could be exceeded.

The situation then abated, but around 250 people have died in floods and landslides over the past fortnight alone, renewing fears with the flood season due to stretch on for several more weeks.