Signs of life were detected in the ruins of a skyscraper in Bangkok on Monday as efforts intensified to find people trapped there three days after a massive earthquake in Southeast Asia that has killed at least 2,000.

Scanning machines and sniffer dogs were deployed at the unfinished skyscraper and Bangkok's Deputy Gov. Tavida Kamolvej said rescuers were urgently working out how to access an area where signs of life had been detected, three days on from the quake.

Realistic chances of survival diminish after 72 hours, she said, adding: "We have to speed up. We're not going to stop even after 72 hours."