Police officers block the access to the Champs Elysees in Paris after a shooting. (AFP)

One police officer was killed and two others wounded Thursday in a shooting on Paris's famed Champs Elysees, just days ahead of France's presidential election, police said. France's interior ministry said the gunman was killed after opening fire on the officers at around 9:00 pm (1900 GMT) on the boulevard. Anti-terror prosecutors have opened an investigation. "The attacker arrived by car and got out. He opened fire on a police car with an automatic weapon, killing one of the police officers and trying to attack others while running," a police source told AFP, asking not be named.The bustling shopping street in the heart of the city was blocked by armed officers and nearby metro stations closed.The election has long been seen as a potential target of jihadists. Witnesses recounted scenes of panic as people ran for cover and sought shelter."We had to hide our customers in the basement," Choukri Chouanine, manager of a restaurant near the site of the shooting, told AFP, saying there was "lots of gunfire."Dozens of vehicles from the emergency services were sent to the area, where a helicopter was also deployed.As the first details filtered through, US President Donald Trump sent his condolences and said that "it looks like another terrorist attack. What can you say? It just never ends."The shooting comes two days after the arrest of two men in southern Marseille with weapons and explosives who were suspected of preparing an attack to disrupt the first-round of the presidential election on Sunday.France is in a state of emergency and at its highest possible level of alert since a string of terror attacks that began in 2015, which have killed over 230 people.Up until now, polls showed voters more concerned about unemployment and their spending power than terrorism or security, though analysts warned this would change in the event of further bloodshed.Far-right leader Marine Le Pen welcomed security moving to the heart of the campaign on Thursday as she took part in a prime-time interview show alongside the 10 other presidential candidates."We are suffering the consequences of a laxity that has continued for years," she said shortly before the shooting, promising to take a hard line against extremists and anyone suspected of being an Islamist.For weeks, centrist former banker Emmanuel Macron and the National Front's (FN) Le Pen have been out in front but opinion polls now show there is a chance that any of four leading candidates could reach the second-round runoff on May 7.Though Le Pen and Macron are the frontrunners, scandal-plagued conservative Francois Fillon and far-left firebrand Jean-Luc Melenchon have closed the gap substantially in the last two weeks."The first responsibility of the president is to protect," Macron said on the interview show. "This threat will be part of our daily lives in the next years."Major attacks in France targeted the Charlie Hebdo magazine in January 2015, sites around Paris including the Bataclan concert hall in November the same year and families at a fireworks display in Nice in July last year.In between, there have been a series of smaller attacks, often targeting security forces.Thousands of troops and armed police have been deployed to guard tourist hotspots such as the Champs Elysees or other potential targets including government buildings and religious sites.In February, a man armed with a machete in each hand attacked soldiers on patrol at Paris's Louvre Museum. The attacker, a 29-year-old Egyptian, was seriously injured.

And in March, a 39-year-old man was killed at Paris's Orly airport after attacking a soldier.