A police officer has died and two others were seriously wounded after a gunman opened fire at the Champs Elysees in Paris.
Paris police said that the attacker targeted police guarding the area near the Franklin Roosevelt subway station at the centre of the avenue on Thursday evening.
One policeman was killed and two others were wounded in the shooting, which Isis has claimed responsibility for.
The gunman, who used a kalashnikov, was shot dead by officers.
Police said a search was underway at his home east of Paris on Thursday night while authorities said a second suspect may still be on the loose and a warrant has been issued for his arrest
French prosecutors have opened a terrorism investigation into the attack.
Islamic State has said one of its "soldiers" carried out the atrocity, naming him as a Belgian man called Abu Yusuf al-Beljiki.
According to French officials, the gunman was already known to security services and had been flagged as an extremist.
The French Interior Ministry said the officers appeared to have been deliberately targeted.
Pierre-Henry Brandet, from the ministry, told reporters: "An automatic weapon was used against police, a weapon of war."
He said the shooting started shortly after 9pm when a car stopped alongside a stationary police vehicle.
Mr Brandet said: "A man immediately got out and opened fire on the police car, fatally wounding a police officer .
"He also wounded a second one, it would seem very seriously."
Armed police were deployed to the landmark after the shooting.
One witness told French television station BFM that she heard gunshots, saw a man's body on the ground and the area was quickly evacuated by police.
Badi Ftaiti, 55, said he saw people fleeing from the avenue as the shots rang out.
He said: "Some were crying. There were tens, maybe even hundreds of them."
Another witness said: I came out of the Sephora shop and I was walking along the pavement.
"A man got out of a car and opened fire with a kalashnikov on a policeman.
"The policeman fell down. I heard six shots, I was afraid.
"I have a two year-old girl and I thought I was going to die. He shot straight at the police officer."
Local authorities told people to avoid the area as it was placed on lockdown on Thursday night.
A police helicopter was seen flying low over the area.
Police and soldiers sealed off the area, ordering tourists back into their hotels and blocking people from approaching the scene.
Emergency vehicles blocked the wide avenue that cuts across central Paris between the Arc de Triomphe and the Tuileries Garden, normally packed with cars and tourists.
The attack came three days before the first round of France's tense presidential election.
Security is high preceding the vote after police said they arrested two men Tuesday in what they described as a thwarted terror attack.
The UK Foreign Office said: "The British Embassy is in contact with local authorities and urgently seeking further information following reports of a shooting incident on the Champs-Elysees in Paris.
"You should remain vigilant and follow the advice of the local security authorities and/or your tour operator.
"If you're in the area and it is safe to do so, contact your friends and family to tell them you are safe."