Investigators are calling an explosion at an apartment home in Grand Rapids "suspicious".

The home is located in Heritage Hill in the 100 block of Union Ave near Fountain Street.

Residents told WOOD TV the explosion shook their unit and started a fire on Saturday. The explosion was powerful enough to blow windows out of the multi-tenant dwelling.

Firefighters are concerned about some of those who lived inside who are unaccounted for.

 Authorities have started to check local hospitals to see if they might've ended up there.

A search of the apartment did turn up drug paraphanelia including butane gas, however authorities do not suspect this was a meth lab explosion.

The investigation remains open, but authorities say the fire burned so hot it will be hard to find the exact cause.

Anyone with information is asked to call Grand Rapids Police or Silent Observer.

Photo courtesy of WOOD TV