Nixon's executive order puts the St. Louis County Police Department in charge of a unified law enforcement command.
In a news release, the governor said that the county police, the St. Louis Police Department and the Missouri Highway Patrol will operate together "to keep members of the public safe and protect property
while allowing citizens to exercise their constitutional rights."
Nixon authorized Stephen Danner, adjutant general of the National Guard, to call portions of the guard into service as needed.
The order will expire in 30 days unless extended.