A curfew instituted in Detroit to keep people who live outside the city from instigating violence during protests over the death of George Floyd began Sunday with police volleying tear gas into a crowd of protesters who refused to disburse.

As the city’s 8 p.m. curfew began, hundreds of people chanting “No Justice, No Peace” in protest of the death of Floyd, a handcuffed black man who died last week after a white Minneapolis officer pressed his knee into his neck as he pleaded for air, amassed outside Detroit police headquarters, The Detroit News reported. Officers stationed themselves in front of the headquarters.

By 8:45 p.m., police marched through downtown streets, firing tear gas and making arrests. Crowds scattered after gas was deployed.

Police gathered near the Rosa Parks Transit Center, firing rubber bullets down Michigan Avenue that could be heard ricocheting off cars.

Detroit’s curfew extends to 5 a.m. Monday. Residents going to and from work will be exempt, and city buses will run their normal routes.

Meanwhile, police continue investigating whether rock throwing and other attacks on officers have been orchestrated by outsiders, according to Mayor Mike Duggan.

Other cities across the U.S. have started similar measures after consecutive days of demonstrations were marked by fights, theft, property damage and attacks on police officers.

“This isn’t intended for Detroiters,” Duggan told reporters Sunday, adding that the curfew is aimed at keeping people who don’t live in the city from damaging property and confronting officers.

Warnings will be issued first for people violating the curfew. Arrests will follow, officials warned.

“It’s going to stay in place as long as (police chief James Craig) feels there is a threat from people outside the community,” Duggan said.

Sixty people were arrested during demonstrations Friday night and early Saturday morning in Detroit. Of that number, 37 were not from Detroit. Of the 84 people taken into custody Saturday night, 63 don’t live in the city.

Two others live in Tennessee and Ohio, police said Sunday.

“We are investigating potential charges against people who do appear to be planning some serious types of destruction,” Duggan said.

The Detroit protests were among dozens around the country over the death of Floyd and the treatment of blacks by police.

Among the protests in Michigan was one Saturday in Grand Rapids, the second-largest city in the state.

At the state capital in Lansing, a curfew was ordered at 9 p.m. after a daylong protest that at times numbered in the thousands. Michigan State Police arrested one man who was vandalized the Capitol with graffiti, Lt. Brian Oleksyk told the Lansing State Journal.

In ordering the curfew, Mayor Andy Schor said the protest had been mostly peaceful. “Unfortunately, the demonstration has now turned violent,” he said in the statement without elaborating.

The Grand Rapids mayor declared a civil emergency and Gov. Gretchen Whitmer ordered the National Guard to be deployed to assist with curfew enforcement and property protection after scores of businesses were damaged overnight Saturday.

The city’s curfew is in place from 7 p.m. to 5 a.m. and spans 48 hours.

“We implore our residents and visitors to abide by this curfew so we can restore order and protect our residents,” Grand Rapids Mayor Rosalynn Bliss said in a release. “What happened in our city last night is beyond heartbreaking and is unacceptable. Violence, chaos and destruction have no place in our city. This does not represent who we are.”