Fire investigators are working to determine the cause of a fire that heavily damaged a vacant house this morning and spread to two occupied structures in Marshall-Shadeland.

The three-alarm fire was reported at 3:46 a.m. in the 2900 block of Shadeland Avenue.

Flames and heat caused damage to homes occupied on either side of the burning structure, fire Chief Darryl Jones said.

The heat had begun to melt the vinyl siding on one of the homes.

No injuries were reported.

Families and pets were forced from the two adjacent houses, but they were able to return after the fire was extinguished.

The fire caused about $60,000 in damage, investigators said.

Arson investigators are checking out reports that someone had been in the vacant house playing with fireworks before the blaze started.