Authorities on Friday said they don't know what sparked a two-alarm fire that caused damage in the Minneapolis Grain Exchange building earlier this week.

Crews were called to the 138-year-old building at 400 S. 4th St. in downtown Minneapolis around 6:30 p.m. Wednesday and quickly put out the flames. Firefighters broke windows to ventilate the structure that had filled with thick smoke and used water to wash down the area. The building was evacuated.

No one was hurt in the blaze, which was contained to the first floor.

The cause has officially been ruled as undetermined, said Minneapolis Assistant Fire Chief Bryan Tyner.

He said the investigation remains open pending additional evidence that may help determine the cause.

It remains unclear how long the historic building will remain closed.