Utrecht shooting: Three killed after gunman opens fire on Dutch tram

Three people were killed and nine injured in a shooting in the Dutch city of Utrecht, the mayor said on Monday, adding that authorities were working on the basis of it being a terrorist attack.

"At this stage, we can confirm three deaths and nine wounded, three of them seriously," Utrecht Mayor Jan van Zanen said in a video statement on Twitter.

"We are working on the principle that it was a terrorist attack," he added.

Dutch Prime Minister Mark Rutte had earlier said there were "possible deaths" and that a terrorist motive was "not excluded".

Dutch police released a picture of a Turkish-born man they are hunting over a shooting on a tram in Utrecht on Monday that left one dead and several injured.

"The police are asking you to look out for 37-year-old Gokmen Tanis (born in Turkey) in connection with the incident this morning," Utrecht police said on Twitter, adding: "Do not approach him."

The Dutch anti-terror coordinator has raised the threat alert to its highest level around the central Dutch town of Utrecht following the shooting incident on a tram in the city, with the shooter still on the run. 

Anti-terror coordinator Pieter-Jaap Aalbersberg said in a statement that the "threat level has gone to 5, exclusively for the Utrecht province," referring to the highest level. 

"The culprit is still on the run. A terror motive cannot be excluded," he said in a Twitter message. He called on citizens to closely follow the indications of the local police. 

German police say they have upped surveillance on the country's border with the Netherlands and are on the lookout for the gunman behind a shooting in the Dutch city of Utrecht.

Heinrich Onstein, a spokesman for the federal police in the border state of North Rhine-Westphalia, told The Associated Press on Monday that additional police had been added to watch not only major highways, but also minor crossings as well as railway routes.

He says the federal police are in close contact with authorities in the Netherlands and have a description of the suspect.