A woman and her dog have been rescued unharmed after falling into a six-metre-deep sinkhole that opened up in her backyard, a Portland fire official said.

Portland Fire & Rescue Lt. Rich Chatman said the woman in her thirties was trying to find her small poodle mix Tuesday night in her dark Portland backyard when she fell into a sinkhole about one metre in diameter. A neighbour who heard her calls for help called 911.

Fire crews used rope and ground ladders to rescue them. Chatman said fire officials at the scene were amazed that both escaped unhurt.

The spokesman said a neighbour who shares a property line said both homeowners had been required to do some recent work on their sewage system.

Crews were covering up the hole temporarily late Tuesday.