Police officers block access to the Champs-Elysées in Paris after a shooting on Thursday, April 20. One police officer and an attacker were killed, according to CNN affiliate BFMTV and the French Interior Ministry. LUDOVIC MARIN/AFP/Getty Images

Bystanders raise their hands in the air as they approach police who were clearing the streets around the Champs-Elysées. FRANCK FIFE/AFP/Getty Images

Emergency crews work near the site of the shooting. FRANCK FIFE/AFP/Getty Images

Police survey the Champs-Elysées as they work to secure the area. Jeff J Mitchell/Getty Images

People evacuate passers-by from the scene with their hands raised. The Champs-Elysées, a top tourist attraction in Paris, is lined with restaurants, cafes, exclusive designer boutiques and tourist shops. Thibault Camus/AP

A forensic team investigates the scene where an attacker opened fire on police with an automatic weapon. Kamil Zihnioglu/AP

A French soldier stands guard after the shooting. THOMAS SAMSON/AFP/Getty Images

A police van is towed away from the scene. Pacific Press/LightRocket via Getty Images

Police, who are on high alert, monitor the scene of the shooting. Thibault Camus/AP

Authorities closed the world-famous shopping street and told people to avoid the area. FRANCK FIFE/AFP/Getty Images