Local fire department chief Thein Tun Oo said the rescue mission was at a critical stage, with the chances of finding the remaining workers alive getting slimmer by the hour.
"I cannot hear any sounds," he said by phone. "There is less chance of survival for the rest."
Video streamed live on Facebook showed firefighters operating heavy machinery to try to shift lumps of concrete and mangled metal to enable rescue teams to search for the missing construction workers.
The accident at the commercial building site appeared to have occurred while 11 workers were laying a concrete slab, Thein Tun Oo said.