Emergency crews say a fire that destroyed a home under construction in the city's west end is being treated as suspicious.

The fire broke out at a home under construction on Joicey Boulevard, in the Avenue Road and Wilson Avenue area, around 3 a.m.

When fire crews arrived, the house was fully engulfed in flames. Toronto Fire says the roof and walls of the home were caving in.

Police say the fire is being treated as suspicious because witnesses reported seeing someone leaving the scene of the fire.

There are no reported injuries.

Officials say 50 firefighters and 13 firetrucks responded to the three-alarm blaze.

Crews will remain on scene during the day to monitor hotspots. 

Office of the Fire Marshal has been called in to investigate.