Qian Gang, author of the book Tangshan Earthquake, said 72-hourperiod was just an average time, as many people had survived for much longer.
Qian, who spent ten years interviewing survivors of the Tangshan earthquake that claimed more than 240,000 lives in 1976 in Hebei Province, said it was possible that people could live after being buried for more than eight days if they had the will to survive.
He cited the case of an elderly woman who drank her own urine to sustain her for 13 days until rescuers pulled her out of the debris.
Reaching to remote villages
On Sunday, President Hu asked rescuers to use "every available means" to reach every village affected by the earthquake.
"We must try every method to send rescuers to every quake-hit village, instead of just working in towns and cities, since a large number of soldiers have entered the quake-hit regions," said Hu, while visiting Yinghua township of Shifang city.
"We must send rescue teams, carrying food and drinking water, to the worst-hit villages, even on foot, as soon as possible," Hu said, traveling on bumpy roads to visit one quake-hit villages to another, comforting victims and encouraging rescuers.
He was surrounded by wailing women when he visited a temporary shelter camp at Yinghua.
"I know you lost family and property. I share the pain with you," he said. "We will try every effort to save your people once there is the slightest hope and possibility."
Hu also hugged an 8-year-old boy when visiting a family in the camp and told him, "You must learn to be brave and not to surrender to difficulties even if you are a child. We shall have confidence, courage and strength."
Walking over the rubble of a fertilizer factory building, Hu told the rescuers working at the site that every trapped person was counting on them and they should seize every second to work as time was limited.
"I truly believe that the heroic Chinese people will not yield to any difficulty!" he shouted to a group of rescuers.