Nixon, who had declared a state of emergency for the town on Saturday and ordered that the streets be cleared for a curfew that ran from midnight to 5 a.m., said the National Guard would fall under the supervision of the Missouri Highway Patrol.
But retired local business owner Marshall Tucker said: "It ain't getting no better with the National Guard coming in. That'll be worse," he said. "Tonight it's going to get really sticky."
As daylight was coming to an end on Monday, police with plastic handcuffs took positions and tried to clear a main thoroughfare where protests have taken place at night, directing crowds into designated protest areas.
Video from the scene showed one journalist, with cameras slung around his neck and his hands bound behind him, being led off by police. He was identified by colleagues as Getty photographer Scott Olson.
President Barack Obama said he told the governor that the National Guard use should be limited and urged healing instead of violence. Attorney General Eric Holder will travel to Ferguson on Wednesday, Obama added.
"While I understand the passions and the anger that arise over the death of Michael Brown, giving into that anger by looting or carrying guns, and even attacking the police only serves to raise tensions and stir chaos. It undermines rather than advancing justice," Obama told a news conference.
The president met with Holder on Monday to discuss the unrest. Holder said more than 40 FBI agents were canvassing Ferguson neighborhoods in an investigation that included federal and local officials.
"Moreover, at my direction, an additional medical examination is being performed on the body of Michael Brown," Holder said. Results of official autopsies by federal authorities and the county are pending.
An autopsy conducted on behalf of Brown's family showed he was shot at least six times, including twice in the head. The path of one bullet indicates the 18-year-old may have been lowering his head in surrender when the fatal shot hit, according to Brown family attorney Daryl Parks.
Parks told a news conference one bullet hit Brown in the very top of his head and another shattered his right eye.
"His head was in a downward position," Parks said. "Given those kind of facts, this officer should have been arrested," Parks said.
There were no signs of struggle with the officer and no gunshot residue on the body.
According to police, the officer involved in the shooting said he fired initially after Brown reached into his police car.
Darren Wilson, 28, the officer who shot Brown as the teenager was walking through a Ferguson residential neighborhood on Aug. 9 with a friend, was put on paid administrative leave and is in hiding.
Edward Magee, a spokesman for the St. Louis County prosecutor’s office, said the case could be presented this week to a grand jury, which will decide whether Wilson will be indicted.
The National Bar Association, the country’s largest network of black attorneys and judges, filed a lawsuit on Monday against the city of Ferguson and its police department over evidence related to Brown’s shooting.
The suit asks the department to preserve all videos, photographs, police logs and investigative reports about the shooting, as well as arrest reports for protesters who were detained in the days and nights that followed.
The shooting set off protests in Ferguson, whose population of about 21,000 is mostly black. Thousands of demonstrators, angry that the police officer was not arrested, have filled the streets.
The protests have been marred by rioting and looting, leaving some stores badly damaged, as well as attacks against police with Molotov cocktails, officials said
Law enforcement officials have been widely criticized for using excessive force. U.N. Secretary-General Ban Ki-moon urged U.S. authorities to protect protesters' rights to peaceful assembly and freedom of expression.
According to accounts by local police, Brown and a friend were walking down a road when Wilson asked them to move onto the sidewalk. Wilson reported that Brown reached into his patrol car and struggled for his service gun when the officer fired the initial shot.
Brown's friend Dorian Johnson, 22, said Wilson had reached out through his car window to grab at Brown and the teenager was trying to get away when he was shot. Johnson said Brown held up his hands to surrender but that Wilson got out of his patrol car and shot him several more times.