Concrete is being used to fill two so-called "sink holes" that are threatening the stability of homes in Lake Macquarie near Newcastle.

The first hole opened up underneath a three-storey home on Lambton Parade at Swansea Heads, forcing the residents inside to evacuate last night.

Emergency crews were called when neighbours noticed the hole had caused the front corner of the house to sink, extensively damaging the property.

Concrete is being used to plug the two holes. ( Jackson Vernon ABC News )

The hole is about 7 metres wide and 5 metres deep, and is believed to be a disused mine shaft.

A second sink hole, which is a few metres wide, opened up in the front yard of a neighbouring property this morning.

The Mine Subsidence Board is using concrete to fill the holes.

University of Newcastle engineering professor Stephen Fityus says he does not think the neighbourhood should be concerned.

"If there's one big shaft in this particular area it's unlikely there'll be dozens of them, that's not the way coal mines work," he said.

"Coal mines are usually horizontal features and so when things collapse they tend to collapse over a relatively short, vertical height and occasionally shafts go back to the surface.

"This is probably an anomaly than anything that's likely to be a trend of more things to come."

Engineers are assessing the first house where a "sink hole" has opened up, threatening its stability. ( ABC News: Jackson Vernon )

Dennis Thompson's house is between the two properties affected by the sink holes.

He and his wife made the discovery when they went outside this morning.

"My wife got up this morning to water the grass and after the meter turned off she could still here it ticking over," he said.

"So we went back out to investigate, and low and behold there's a hole in this side of the property as well.

"So immediately I went and notified the neighbour who came out and very casually said 'I better do something about it'."

Mr Thompson said it was quite a shock.

"We've never had a problem here in the past, even when we had the earthquake there was very little damage done out here," he said.