Two police officers have been shot and killed on Paris' Champs Elysees but it is too early to say what the motive was, French Interior Ministry spokesman Pierre-Henry Brandet says.
Police sources initially said the shooting could have been an attempt at an armed robbery.
Paris police said the gunman killed two police officers before being killed himself.
A police source told Reuters there had been two assailants, while a witness saw one man get out of a car at the scene and begin shooting with a machine gun.
A police union Twitter account tweeted the first police officer was shot while in a car stopped at a red light by an attacker driving by.
Paris police spokeswoman Johanna Primevert told The Associated Press the attacker targeted police guarding the area near the Franklin Roosevelt subway station.
Police authorities urged the public to avoid the area.
A Reuters reporter saw a helicopter flying low over central Paris, apparently part of a follow-up police operation.
The incident came as French voters prepared go to the polls on Sunday in the most tightly-contested presidential election in living memory.
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.
Earlier this week, two men were arrested in Marseille whom police said had been planning an attack ahead of the election.
A machine gun, two hand guns and three kilos of TATP explosive were among the weapons found at a flat in the southern city along with jihadist propaganda materials according to the Paris prosecutor.