A police officer surrounded by a crowd in the US state of Washington struck and injured at least one person with his car as he sought to drive away, authorities said.

About 100 people and several cars were blocking an intersection, reportedly for an illegal car rally, on Saturday night in downtown Tacoma when police were called to the area.

After an officer in his car tried to clear the area, a crowd began hitting the vehicle's body and windows, Tacoma police said in a statement.

"While trying to extricate himself from an unsafe position, the officer drove forward, striking one individual and may have impacted others," the police said, adding that the person was taken to a hospital in unknown condition.

Tacoma resident Sarah Jones told CBS she witnessed the scene that included a "mountain of people" being hit.

"I don't know if he panicked or what but his car was surrounded," Jones said of the policeman. 

"I turned my back for one second and when I turned it back around, I saw the cop car roll over a mountain of people," she said.

Police use of force is a particularly sensitive issue in the United States, which in recent months saw nationwide protests over police brutality towards Black people.

"I send my thoughts to anyone who was injured in tonight's event, and am committed to our department's full cooperation in the independent investigation," Tacoma police chief Mike Ake said in statement.