Live updates on this breaking story
Armed police have blocked off the Champs Elysees in Paris after an officer was killed and another wounded in a shooting.
The officer was said to have been killed while in a car stopped at a red light.
A report citing a police source said the person who fired on officers had been killed in turn. There were at least two attackers.
Police said the shooting was very probably a “terrorist act”, according to Reuters, while other reports suggested robbery may have been the motive. The French interior ministry said it was too early to judge the reason behind the attack.
It came just days before French voters were set to go to the polls in the first round of the presidential election.
Police urged people to avoid the area.
A witness identified only as Ines told French television station BFM that she heard a shooting and saw a man's body on the ground, and that the area was quickly evacuated by police.
Another reportedly said they saw a man get out of a car and begin firing a Kalashnikov rifle.
A third witness told local media: “Suddenly everyone got up and started running, we didn't even have the time to understand what was happening.
“We heard one or two gunshots, it wasn't a Kalashnikov, it was shot by shot. We ran. I really didn't understand what was happening, we moved down the street, police told us to move down further.
“I didn't see if they were two, three or just one assailant. We just ran.
“We heard two gunshots. All the people sat on the terrace got up and ran, chairs were falling over.”
Paris police spokeswoman Johanna Primevert said the attacker targeted police guarding the area near the Franklin Roosevelt subway station Thursday night, at the centre of the avenue popular with tourists.
France has lived under a state of emergency since 2015 and has suffered a spate of Islamist militant attacks that have killed more than 230 people in the past two years.
More follows
