In this image made from video, emergency services arrive on the scene of a Christmas market in Strasbourg, France, Dec 11, 2018. (PHOTO / AP)

STRASBOURG, France — French authorities detained five people as they hunted Wednesday for a suspected extremist who sprayed gunfire at one of Europe's most famous Christmas markets in the eastern city of Strasbourg, killing three and wounding at least 13 and putting the whole country on edge anew.

Police identified the suspect as Strasbourg-born Cherif Chekatt, 29, who was known to the intelligence services as a potential security risk

Police detained five people in overnight searches around the city, Laurent Nunez, secretary of state for the Interior Ministry, said on France-Inter radio.

"The hunt is continuing," Nunez said on France Inter radio. Asked whether the suspect might have left France, he said: "That cannot be ruled out."

A terrorism investigation was opened, but the motive of the attack is unclear. Nunez said eight of the injured are in serious condition, and the city mayor said some had head wounds.

French Interior Minister Christophe Castaner on Wednesday said that 350 security agents were hunting for the gunman who fled the scene. 

"He fought twice with our security forces," Castaner told a news conference held in the city. 

Castaner said France was raising the security threat level and would bolster the protection of Christmas markets elsewhere and strengthen border controls.

France's Interior Minister Christophe Castaner, center, speaks during a press conference in Strasbourg, eastern France, Dec 11, 2018. (JEAN-FRANCOIS BADIAS / AP)

The shooter was shot and wounded by soldiers guarding the Christmas market, according to Stephane Morisse of police union FGP Police.

Police identified the suspect as Strasbourg-born Cherif Chekatt, 29, who was known to the intelligence services as a potential security risk. 

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No one immediately claimed responsibility, but the US-based Site intelligence group, which monitors jihadist websites, said Islamic State supporters were celebrating.

The attack is a new blow to France, after a wave of Islamic extremist killings in 2015 and 2016, and amid a month of protests against President Emmanuel Macron that have blocked roads around the country, led to rioting in the capital and put a heavy strain on police.

While authorities urged people in the area to stay inside after Tuesday's attack, Strasbourg Mayor Roland Ries told BFM television Wednesday that "life must go on" so that the city doesn't cede to a "terrorist who is trying to disrupt our way of life."The assailant got inside a security zone around the venue and opened fire from there, Mayor Roland Ries said on BFM television.

Shooting near a Christmas market in Strasbourg, France. (GRAPHIC / AFP)

One possible reason for the attack: police tried and failed to arrest him earlier Tuesday for an attempted murder, Nunez said. The suspect had been identified as radicalized during past stays in prison, Nunez added. Authorities did not identify him publicly.

Police were out in force in Strasbourg on Wednesday morning, and the Christmas market was closed. Strasbourg, a city about 500 kilometers east of Paris on France's border with Germany, promotes itself as the "Capital of Christmas" and the market set up around the local cathedral is a holiday tradition. The market was the target of an al-Qaida-linked plot at the turn of the millennium.

Many of Europe's deadliest terror attacks in recent years have taken place in France.

"I heard two or three shots at around 7:55 pm, then I heard screams. I got close to the window. I saw people running. After that I closed the shutters. Then I heard more shots, closer this time," said Yoann Bazard, 27, who lives in central Strasbourg.

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Basketball supporters wait to leave after a match at the Rhenus Sport stadium in Strasbourg, eastern France, Dec11, 2018. (JEAN-FRANCOIS BADIAS / AP)

"I thought maybe it's firecrackers," he said, speaking by phone. "And then, as it got close, it was really shocking. There were a lot of screams. ... There were police or soldiers shouting 'Get inside!' and 'Put your hands on your head.'"Another witness, Peter Fritz, told the BBC one of the three people killed was a Thai tourist who was shot in the head and didn't respond to lengthy attempts to revive him.

In this image made from video provided by CMM, people lay on the ground after a shooting at a Christmas market in Strasbourg, France, Dec 11, 2018. (PHOTO / CMM / AP)