Chicago cop shot multiple times, in 'grave' condition

An off-duty officer with the Chicago Police Department remains in "grave condition" Tuesday afternoon after he was reportedly shot multiple times in a building downtown.

"CPD officer assisting a tactical team and was shot by assailant," the department tweeted, adding that the officer was transported to Northwestern Memorial Hospital.

The officer, identified as a district commander, was shot in the stairwell of the Thompson Center in the city's downtown business center, Fox 32 Chicago reported.

One person has been taken into custody for questioning, police spokesman Anthony Guglielmi told The Associated Press. It's unclear if that person is a suspect in the shooting.

Police were seen blocking off the building, which houses state government offices.

This is a developing story. Check back for updates. Fox News' Matt Finn and The Associated Press contributed to this report.

Nicole Darrah covers breaking and trending news for FoxNews.com. Follow her on Twitter @nicoledarrah.