Rescue teams fought gusty winds and altitude sickness Thursday as survivors faced a second night outside in freezing weather after strong earthquakes left more than 600 dead and 9,000 hurt in a mountainous Tibetan area of western China.

Rescuers, tired from the high winds and thin oxygen, pulled survivors and more bodies from the pulverized remains of the town flattened by Wednesday morning's quake, the largest of which was magnitude 6.9. About 15,000 houses have collapsed.

"We've seen too many bodies and now they're trying to deal with them. The bodies are piled up like a hill. You can see bodies with broken arms and legs and it breaks your heart," said Dawa Cairen, a Tibetan who works for the Christian group the Amity Foundation and was helping in rescue efforts. "You can see a lot of blood. It's flowing like a river."

Zou said that 617 died in the quake, with 313 missing and more than 9,100 hurt.

Wednesday morning's quakes -- the worst of which measured magnitude 6.9 by the U.S. Geological Survey and 7.1 by China's earthquake administration -- were the worst to hit the region since the massive Sichuan earthquake two years ago left 90,000 dead or missing.