A scanner has detected 70 signs that could be missing people deep inside the rubble of the collapsed State Audit Office building in Bangkok.

The sensor, supplied by the US military, detected the signs in the centre of the collapsed building, between the 17th and 21st floors where most of the missing people had been working when the earthquake struck on Friday.

Bangkok deputy governor Tavida Kamolvej said it was unclear whether all 70 signs were missing people. However, six had been identified as human bodies. 

The building had collapsed floors lying on top of each other, so it was not known which floor each person was on, she said. 

Rescuers said they were making the best progress they could, but admitted it was a struggle to get to the trapped people.

The walls were about one metre thick, making excavation difficult.

The site is still too unstable to use heavy excavating equipment. Workers have had to gradually remove the debris, lifting and clearing it from the top down. 

The Bangkok Metropolitan Administration (BMA) said at 8am Tuesday that the confirmed toll from the collapse was 13 dead and 19 injured, with scores still missing. Seven other deaths linked to Friday’s quake were reported at other locations.