FERGUSON, Mo. — Violence erupted here once more overnight, even as Missouri National Guard troops arrived, the latest in a series of quickly shifting attempts to quell the chaos that has upended this St. Louis suburb for more than a week.

In the days since an unarmed black teenager, Michael Brown, was shot to death by a white police officer here on Aug. 9, an array of state and local law enforcement authorities have swerved from one approach to another: taking to the streets in military-style vehicles and riot gear; then turning over power to a Missouri State Highway Patrol official who permitted the protests and marched along; then calling for a curfew.

Early Monday, after a new spate of unrest, Gov. Jay Nixon said he was bringing in the National Guard. Hours later, he said that he was lifting the curfew and that the Guard would have only a limited role, protecting the police command post.

Although the tactics changed, the nighttime scene did not.

Late Monday night, peaceful protests devolved into sporadic violence, including gunshots, by what the authorities said was a small number of people, and demonstrators were met with tear gas and orders to leave. Two men were shot in the crowd, officials said in an early-morning news conference, and 31 people — some from New York and California — were arrested. Fires were reported in two places. The police were shot at, the authorities said, but did not fire their weapons.