The fire that shut down cross-Bay BART service Thursday may have been intentionally lit, Oakland fire officials said.

The blaze began about 2:18 a.m. in a senior housing project that was under construction. It spread to tracks near the West Oakland BART station.

Oakland Battalion Chief Lisa Baker said a security guard was on the property moments before the fire started. She would not confirm the number of suspects, but said suspicious activity occurred in the area.

She asked anyone with information to call (510) 238-4031.

The blaze, which was contained about 6:30 a.m., caused roughly $1 million in damage to the construction site.