An earthquake survivor trapped in a collapsed hotel in western Indonesia sent a text message saying he and some others were alive, triggering a frantic rescue operation, but hopes faded today as sniffer dogs failed to detect life.

Padang's police chief said voices and claps were heard from survivors buried in the Ambacang Hotel since Wednesday's 7.6-magnitude quake, which killed at least 715 people. He said one survivor – who had been staying in room 338 – sent a text message to relatives Friday, saying he and some others were still alive.

"We estimate there are still eight people trapped alive under Ambacang Hotel," colonel Boy Rafli Amar told reporters. "We are still trying hard to evacuate them." After more than six hours of searching, Amar said, "So far rescuers have found nothing."

Rescuers used backhoes and drills to try and break a passage through the thick slabs of concrete of the six-storey hotel. Hidehiro Murase, the head of a Japanese search-dog team, said its search had been fruitless.

"We did an extensive search this morning, but there were no signs of life. Our dogs are trained to smell for living people, not the dead, and they didn't sense anything," he said.

The quake devastated more than 60 miles along the western coast of Sumatra island, prompting a huge international aid operation in a country that sits on a major geological fault zone.