Police are treating a fire at a de-commissioned Toukley motel as suspicious.

The blaze spread quickly after starting on the top level of the old Waters Edge Motel.

It took firefighters from Toukley, Budgewoi and Hamlyn Terrace two hours to extinguish it.

Traffic along Main Road had to be diverted during that time.

Police are hoping to speak to a number of young people who were seen outside the premises just before the fire ignited.