The capitol building in Springfield was placed on lockdown around 1:30 Thurs.
It happened just as representatives in the House were preparing to debate a possible override of the Governor’s veto of a proposed budget.
Springfield Fire Chief Barry Helmerichs says the building is on lockdown after a woman allegedly threw a powdery substance in the governor's office.
A team of first responders wearing HazMat suits arrived on the scene shortly after the announcement. State Rep. Jehan Gordon Booth posted a Facebook live video saying lawmakers were unable to enter or leave the building until first responders deem the area safe.
As a result, the discussion and vote on the possible override is delayed.
Dave Druker, a spokesman for the Secretary of State's office, which oversees Capitol security, said one person was taken into custody Thursday. He did not have further details.
This story is developing and will be updated.