Story highlights Nine people were arrested

Five officers were injured

May Day protests in Seattle have been marred by violence in recent years

(CNN) May Day protests in Seattle turned violent on Sunday, as protesters lit fireworks and threw rocks and Molotov cocktails at police, Seattle Police said.

After a peaceful march was held earlier in the day, nine people were arrested and five officers were injured in the clashes, according to police.

Seattle Mayor Ed Murray thanked police for their "extraordinary work" in a statement.

"It is unfortunate and deeply regrettable that in a city that goes to incredible lengths to respect First Amendment rights, there are some who disregard our values and engage in senseless acts of violence and property destruction," he said. "My thoughts are with the officers who were injured."

One officer sustained a facial laceration, another was bitten and a third was hit by a Molotov cocktail but not burned.