PORTLAND — A 14-hour census of Maine’s homeless ended after sunrise Wednesday as teams of counters staked out two abandoned buildings in Portland to wait for people to step outside into the damp morning air.

But when no one emerged from either building by 8 a.m., the teams ended their four hours of surveillance, closing the books on an overnight operation that federal Census Bureau workers hailed as a success. Critics said the numbers obtained by the government would not be reliable.

For example, whether there were any homeless in the two vacant buildings remained a mystery. Safety considerations barred census workers from entering abandoned buildings, and officials acknowledged that anyone who spent the night inside and slept late would have escaped detection.

The building stakeout was the final phase of “S Night” — or “street and shelter night” — which began with a six-hour sweep of emergency shelters that was followed by pre-dawn visits to street locations such as parks, bridges, alleys and piers.

The results of the head count won’t be known until next January.