A suspicious fire erupted in a vacant building on a pier in Crockett early Tuesday, sending flames high into sky and illuminating the waterfront below the Carquinez Bridge.

Carquinez Fire District Battalion Chief Don Colombo said the fire was suspicious because there was no obvious cause for the blaze.

“There is no one living on the pier, there is no electricity on the pier, there e are no obvious signs of ignition,” Colombo said.

Witnesses have told authorities they saw what appeared to be a small warming fire -- possibly set by fishermen -- before the one-alarm fire erupted.

Authorities said the fire was first reported at 3:44 a.m. on the pier that was about 80-to-100 years old located near Loring Avenue and Jackson Street.

Arriving firefighters found a large vacant building, jutting about 50 feet over the water, fully engulfed in flames.

Because there were concerned about the safety of the pier itself, the fire proved to be challenging to fight. A fireboat was called in and the land-based firefighters fought it defensively from the exterior.

Colombo said the pier is quite old and was the site of a fire about two years ago.

"The pier is so far gone that the investigation is going to be very difficult," Colombo said.

No injuries have been reported, according to fire officials.