BEIJING, May 19 -- It was more than 72 hours after the quake and no cry for help could be heard from the rubble of Beichuan Middle School amid the din of heavy machinery around.

A rescue team from Chongqing was doing a last search on the school's collapsed main building, giving up hope of any survivors - when a sniffer dog barked.

Firefighters conduct rescue operation with search dogs at Mianzhu of southwest China's Sichuan Province on May 18, 2008.

Rescuers started moving heavy concrete chunks at the spot and two hours later, they found a girl in coma, her legs wounded badly, but still breathing.

She was reportedly the last survivor found in the school.

The efficacy and efficiency of sniffer dogs have become legion in the quake-hit areas of Sichuan, where they are often seen as the last line of hope.

More than 100 are working day and night, searching for signs of lingering life from corners and crevices that are beyond the reach of human senses.

"I've had my dog ever since he was a couple of months old but he's never been in such surroundings - the smell of bodies, the aftershocks and endless noise of power generators and hydraulic machines," said Qi Zhigang, keeper of Si Dao, a 6-year-old black Labrador.