The fire marshal's office is investigating an early morning fire in a Richmond Hill development that has now seen three fires since May.

Firefighters were called to a group of houses on Gracedale Drive near Yonge Street and Elgin Mills Road just before 5 a.m. Monday morning where they found two homes ablaze.

The homes are all under construction, but the two that were ablaze Monday morning were nearly complete.

Richmond Hill Fire Chief Steve Kraft said one of the homes will likely have to be torn down now. 

Last week there was another fire at one of the same homes but crews were able to extinguish it in time.

Also in late May eight houses in the new subdivision were damaged by fire, some extensively.

Kraft said preliminary findings point to welding equipment that accidentally started that blaze.

"Right now we don't think there's a link between the fire in May to the two houses that were on fire today but we are treating the fire today as suspicious," he said.

The fire was put out within an hour and no one was injured.