MOUNTLAKE TERRACE, Wash. -

An early morning fire has heavily damaged the Mount Zion Lutheran Church in Mountlake Terrace.

Firefighters responded to the church at 21428 44th Ave. West at around 4 a.m. Wednesday after receiving reports of smoke and flames coming from the building.

Flames were about 20 feet high when firefighters arrived. They cut holes in the roof and sprayed water on the fire to extinguish it.

In the aftermath, half the church's roof is gone and the interior of the building suffered major damage. The flames destroyed the chapel and the administration area of the church.

Fire crews searched the building to make sure no one was inside. One firefighter was injured when he was struck by a chunk of sheet rock that came loose.

Fire investigators initially discovered what they thought was an incendiary device behind the building - but it was later determined that it was just rubbish unrelated to the fire.

The investigation continues, and officials now say it appears the blaze started on the building's exterior.

"Right now ... they're pretty sure it started on the outside of the building," says Jerry Sheehan of the Snohomish County Fire District.

The church pastor, Rev. Frank Payne, says he doesn't know of any reason someone would want to start his church on fire. He says the building is insured and, right now, he's focusing on moving forward.