Sources:AAP | Associated Press
Paris police officials say the chief suspect for the attack on the Champs-Elysees which killed one police officer and seriously wounded two others before police shot and killed the attacker was a 39-year-old from a suburb east of Paris.
Authorities have declined to name him as they hunt for a possible accomplice.
Police have raided at least one location in an eastern Paris suburbs.
ISIS quickly claimed responsibility for the attack.
Paris police spokeswoman Johanna Primevert told The Associated Press that the attacker targeted officers guarding the area near the Franklin Roosevelt subway station at the centre of the sparkling shopping boulevard popular with tourists.
Police and soldiers sealed off the area, ordering tourists back into hotels and blocking people from approaching the scene.
The attack came three days before the first round of balloting in France's tense presidential election.
Security has been especially high since Tuesday, when police said they thwarted a terror attack by arresting two men.
The Paris prosecutor's office said counter-terrorism investigators are involved in the probe of today attack. Two police officials said the attacker had been flagged as an extremist. They had no other details about him.
The claim of responsibility several hours after the attack came unusually swiftly for the ISIS, which has been losing territory in Iraq and Syria.
In a statement from its Amaq news agency, the group gave a pseudonym for the shooter, Abu Yusuf al-Beljiki, indicating he was Belgian.
Soon after the Arabic language statement, the group sent one out in French, describing it as an attack "in the heart of Paris."
Officers 'deliberately targeted'
Interior Ministry spokesman Pierre-Henry Brandet said on BFM television that a man came out of a car and opened fire on a police vehicle. He said officers were "deliberately" targeted.
Speaking in Washington during a news conference with Italian Prime Minister Paolo Gentiloni, US President Donald Trump said the shooting "looks like another terrorist attack" and sent condolences to France.
Emergency vehicles blocked the wide avenue lined with shops that cuts across central Paris between the Arc de Triomphe and the Tuileries Gardens, normally packed with cars and tourists. Subway stations were closed off.
'They were running'
The gunfire sent scores of tourists fleeing into side streets.
"They were running, running," said 55-year-old Badi Ftaïti, who lives in the area. "Some were crying. There were tens, maybe even hundreds of them."
Security forces are more widespread in Paris since deadly Islamic extremist attacks in recent years, and France remains under a state of emergency.
French President Francois Hollande held an emergency meeting with the prime minister today and planned to convene the defence council tonight.
The incident recalled two recent attacks on soldiers providing security at prominent locations around Paris: one at the Louvre museum in February and one at Orly airport last month.
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 before police quickly evacuated the area where she works in a shop.
A French television station hosting a televised event with the 11 candidates running for president briefly interrupted its broadcast to report the shootings.
None of the candidates immediately commented.