The two holes, the first of which appeared on Tuesday night and the second on Wednesday morning, are believed to have formed from the furnace shaft of a disused mine.

The first sinkhole was noticed at a house on Lambton Parade and opened to a width of 20m and a depth of 10m. The second, smaller sinkhole was noticed yesterday morning.

A three-storey home started sliding into the large sinkhole, which had opened up in its front yard. The house is now being stabilised to prevent further slippage.

Contractors working for the MSB had pumped about 35cu.m of concrete into the first hole and were ready to pump in further grouting if required. The MSB is waiting the second hold is stabilised before grouting that, too.

The street was built over the Swansea Pit, a coalmine that was abandoned in the 1950s, but which had no recent history of subsidence, according to the MSB.

MSB chief Greg Cole-Clark told Fairfax Media that he believed that the problem had been contained and no other houses in the street were in danger of collapsing.

“We are now in the process of securing the site,” Cole-Clark reportedly said.

“There are mine workings under the site. They were abandoned about 1953.

“At this point in time, we assume they're about 25m in depth.

“There has been no history of mine subsidence in this area for 60 years or more.”

Cole-Clark said the MSB was monitoring the smaller second hole, which might have resulted from the earlier event.