An old mine shaft has triggered a series of sinkholes to appear in a quiet Australian suburban street threatening million-dollar homes. The first sinkhole, 20m wide and 10m deep, occurred on Tuesday night, next to a luxury home on Lambton Parade in Swansea Heads near Newcastle. The hole developed next to the front deck of the home. However, luckily the home survived. A second sinkhole developed on Wednesday morning in the front garden of a neighbouring property measuring about two meters across. Police said the area underneath the neighborhood was once part of the Swansea Pit, a coal mine abandoned in the 1950s. "It appears what has happened is that an old mine shaft, a furnace shaft, has caused the collapse," Inspector Sam Crisafulli told the Newcastle Herald. The Mining authorities are conducting an investigation checking to see how widespread the sinkhole problem is and its effect on surrounding homes.