Two sinkholes appeared in the luxury waterfront home in the Lake Macquarie suburb of Swansea Heads of Newcastle.

A first sinkhole appeared Tuesday night beside a three-storey home on Lambton Parade. The sinkhole measures approximately 20m wide and 10m deep. A second, smaller sinkhole appeared on Wednesday morning at the garden of another property within two doors from where the first sinkhole developed. The second sinkhole measures two metres across.

The neighbourhood was once part of a coal mine forsaken since the 1950's, the Swansea Pit.

The families affected were safely evacuated from the area and the Mine Subsistence Board is already investigating the incident. They were not yet advised when it is safe to return to their damaged homes.

Greg Cole-Clark, head of Mine Subsistence Board, told press that other properties within the neighbourhood are safe from harm, Newcastle Herald reports. He explained that the sinkholes were "an unusual event."

"We don't have undue concern for any other properties other than those that have been immediately affected. We will continue to do a bit more analysis as time passes. We are now in the process of securing the site. There are mine workings under the site, they were abandoned about1953. At this point in time we assume they're about 25 metres in depth. There has been no history of mine subsidence in this area for 60 years or more. It is an unusual event. We'll have concrete put into it in the next hour or two then look at supporting the home," Cole-Clark said.

The second sinkhole appeared due to "cause and effect", Cole-Clark added.

The homeowner affected by the sinkholes will receive compensation from the Mine Subsidence Compensation Act for the damage. However, Cole-Clark did not comment whether the owners would be compensated for the decreased value of their homes.

Speaking with 1233 reporter Amanda Astri, Dennis Thompson, the owner of the house sandwiched between the two properties affected, said he was pretty casual about the incident.

"I'm pretty casual about it. It was a bit unbelievable. It's a bit of a worry because we're in the middle. I need to talk to one of the mine subsidence guys. We've never had a problem here in the past, even when we had the earthquake there was very little damage done."