By Alister Doyle

OSLO (Reuters) - The crushed skeletons of children point to an earthquake and catastrophic flood on China's Yellow River 4,000 years ago that could be the source of a legendary "Great Flood" at the dawn of Chinese civilization, scientists say.

A Chinese-led team found remnants of a vast landslide, caused by an earthquake, big enough to block the Yellow River in what is now Qinghai province near Tibet.

Ancient sediments indicated that the pent-up river formed a vast lake over several months that eventually breached the dam, unleashing a cataclysm powerful enough to flood land 2,000 km (1,200 miles) downstream, the scientists wrote in the journal Science.

The authors put the Yellow River flood at around 1920 BC by carbon-dating the skeletons of children in a group of 14 victims found crushed downstream, apparently when their home collapsed in the earthquake. Deep cracks in the ground opened by the quake were filled by mud typical of a flood and indicated that it struck less than a year after the quake.

The flood on Asia's third-longest river would have been among the worst anywhere in the world in the last 10,000 years and matches tales of a "Great Flood" that marks the start of Chinese civilization with the Xia dynasty.

"No scientific evidence has been discovered before" for the legendary flood, lead author Wu Qinglong of Nanjing Normal University told a telephone news conference.

In traditional histories, a hero called Yu eventually tamed the waters by dredging, "earning him the divine mandate to establish the Xia dynasty, the first in Chinese history," the scientists wrote.

Their finds around the Jishi Gorge from about 1900 B.C. would place the start of the Xia dynasty several centuries later than traditionally thought, around the time of a shift to the Bronze Age from the Stone Age along the Yellow River.

Some historians doubt the Xia dynasty existed, reckoning it part of myth-making centuries later to prop up imperial rule. Written records date only from 450 BC.

The evidence of a massive flood in line with the legend "provides us with a tantalizing hint that the Xia dynasty might really have existed," said David Cohen of National Taiwan University, one of the authors.

Deluges feature in many traditions, from Hindu texts to the Biblical story of Noah. In pre-history, floods were probably frequent as ice sheets melted after the last Ice Age ended about 10,000 years ago, raising world sea levels.

(Reporting By Alister Doyle; Editing by Janet Lawrence)