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Fire officials have determined that the house explosion in Guelph was caused by an internal gas leak, but the exact source is still being investigated.

The Ontario Fire Marshal's Office says it should wrap up its investigation on Monday afternoon.

Lead investigator Dave Emberlin says the OFM has found where the leak came from, but needs to verify the source by isolating it from other possibilities.

According to Emberlin, Enbridge Gas had been doing work at the house just before it exploded.

"They were here Friday and did a metre change on the house and it was shortly after that that this occurred," he says.

"So I can't tell you exactly where the leak came from at this point, but it's a result of an action that occurred during the metre change out."

The blast on Southcreek Trail rocked a neighbourhood. A woman and her dog were home at the time and managed to escape without physical injuries.

Both neighbouring houses were also damaged in the explosion.

Officials had to inspect them for structural damage before the residents were able to return, but by Monday morning they had been allowed home.