FERGUSON, Missouri - Missouri Governor Jay Nixon has called out the National Guard after another night of trouble in Ferguson, Missouri.

Police used tear gas to clear protesters off the streets late Sunday, a week after demonstrations over the fatal shooting of unarmed black teenager Michael Brown by a white police officer filled the St. Louis suburb with angry, defiant crowds.

Missouri State Highway Patrol Capt. Ron Johnson, whose agency was put in charge of security in Ferguson by Nixon, told reporters early Monday that police had to respond after shots were fired at them and others and several locations were looted or vandalized, including a McDonald's where employees felt the need to lock themselves in a storage room for their safety.

Johnson said Molotov cocktails, bottles and other objects were thrown at police.

At least two injuries resulted from the gunshots, Johnson said, but no officers were hurt. Several people were arrested.

Johnson blamed the latest trouble on a small group of people intent on causing it.

The latest clashes in Ferguson saw another peaceful protest quickly deteriorate.

Three hours before a midnight curfew imposed by Nixon, officers in riot gear ordered all the demonstrators to disperse. Many of the marchers retreated, but a group of about 100 stood defiantly about two blocks away until getting hit by tear gas.

Protesters laid a line of cinder blocks across the street near the QuikTrip convenience store that was burned down last week. It was an apparent attempt to block police vehicles, but the vehicles easily plowed through. Someone set a nearby trash bin on fire, and gunshots rang out several blocks away.

Within two hours, most people had been cleared off West Florissant Avenue, one of the community's main thoroughfares. The streets remained empty as the curfew began.

Nixon's office announced early Monday that, "A day of hope, prayers, and peaceful protests was marred by the violent criminal acts of an organized and growing number of individuals, many from outside the community and state, whose actions are putting the residents and businesses of Ferguson at risk. ... Given these deliberate, coordinated and intensifying violent attacks on lives and property in Ferguson, I am directing the highly capable men and women of the Missouri National Guard to assist ... in restoring peace and order to this community."

There was no immediate indication of how many guard personnel would be involved.