As he lay trapped for some 82 hours under the rubble of his Kathmandu hotel after Nepal's devastating earthquake, Rishi Khanal knew what he must do to survive: drink his own urine.

After a painstaking rescue effort, Nepalese and French emergency workers finally pulled the 28-year-old alive late Tuesday from the wreckage, from where he had been desperately calling relatives on his phone for days.

Dazed and caked in dirt, Khanal was carried out of the wreckage on a stretcher before being taken to hospital where doctors said he was lucky to be alive, suffering a leg injury.

Brother-in-law Purna Ram Bhattarai, 32, described how Khanal was left helpless when his leg was pinned under debris during Saturday's quake that has killed more than 5,000 people.

"He said that the walls just started crumbling, and there was nothing he could do. His leg was stuck and he was trapped," Bhattarai told AFP on Wednesday.

"He said he was so thirsty that he even drank his own urine, there was nothing else, no option," Bhattarai said as he waited at Tribhuwan University Teaching Hospital for Khanal to return from surgery on his leg.

From beneath the rubble, Khanal had called Bhattarai to plead for help.

But Khanal, who has a wife and a six-month-old baby and lives in Arghakhanchi district, had forgotten the name of the hotel where he had been staying since last Thursday.

"You won't believe it, but we could reach him on his phone even after two days," Bhattarai said.

"'I'm trapped here' he said, but in panic he forgot the hotel's name. If he had remembered, maybe we would have found him earlier."

Bhattarai said the phone later went dead, sparking a desperate search of overwhelmed hospitals and mortuaries in the devastated capital.

"We looked everywhere, we went to all the hospitals. Checked patients and even the dead. We had lost all hope of finding him."

"Luck saved him, it's like he has a second life. Everybody else is dead," said Bhattarai.

"He was conscious when he was rescued... he said 'Oh God, thank you'."

"His wife was very relieved when we called her."

Like thousands of other young men who leave impoverished Nepal for work in the Gulf, Khanal had been scheduled to fly to Dubai on Sunday to start at a KFC outlet.

International rescue teams, some using sniffer dogs, have been racing against the clock to find survivors trapped in the rubble of houses and other buildings.

The government acknowledged it had been overwhelmed by the devastation from the deadliest quake in Nepal in over 80 years.

Around 8,000 people were injured while the United Nations estimates that eight million people have been affected.

Hospital chief administrator Parashu Ram Koirala said that apart from the leg injury, Khanal's condition was not thought to be serious.

"When they rescued him, he was conscious and he has been fine otherwise. We are operating on him right now," Koirala told AFP.

"He is very lucky to be alive."