The Las Vegas Strip was blocked off after a car mowed down as many as 20 pedestrians Sunday night, authorities said.

Rows of ambulances gathered at the scene, their lights flickering in the night. A witness described a chaotic scene as people fled.

"Everyone was running ... and as I was running, I saw a car up on the sidewalk coming toward us," a witness told CNN affiliate KLAS. "I saw a lady, she didn't seem like she wanted to stop the car, she had both hands on her wheel and she was looking straight forward."

The witness said people scrambled to stop the driver.

"I saw men running after her, yelling, 'stop, stop!' As she was passing, we saw people running after her. Everyone was so frantic and just running around."

Another witness said people pounded on the car's window.

"The car rolled right in front of me. By the time I looked over to the right, all you could see was [her] driving away and people were bouncing off the front of the car, you can hear it," he said.

"The windshield is smashed at this point. She rode the sidewalk, she came to a stop at the Paris intersection, people are punching into the window ... she accelerated again and just kept mowing people down."

Traffic snaked down the streets as cars were diverted near the Paris Las Vegas hotel, where the Strip was shut down.

No more information was immediately available.

(CNN)