THE Utrecht "gunman" has been arrested after "shooting a relative on a tram for family reasons and opening fire at anyone who tried to stop him".

Cops have detained suspect Turkish born Gökmen Tanis, 37, hours after a shooter opened fire on passengers in a stationary tram on Monday, leaving three dead and several fighting for their lives.

11 Cops have arrested suspect Gökmen Tanis, 37, in connection with the alleged attack Credit: Twitter/police handout

11 An armed cop was seen at the ready as police swarmed a building in search of the suspect Credit: Arjan van Midden / Twitter

11 Special Police Forces inspected the tram after the attack at a crossing in Utrecht Credit: EPA

11 A second police handout also shows Gökmen Tanis on the tram just minutes before the shooting began Credit: Police handout

11 Forensics were seen investigating the tram where a shooting took place this morning Credit: AFP

Netherlands shooting - Dutch PM Mark Rutte makes a statement following attack in Utrecht saying there may be more that one suspect at large

Police earlier released CCTV images of Tanis in a tram apparently taken just four minutes before the shooting broke out at the 24 October Square station at 10.45am.

An earlier figure of nine injured was later revised to six.

Armed terror units surrounded an apartment building where the gunman was holed up two miles from the scene as the shooting initially sparked a lockdown across the city.

Reports from Anadolu news agency claimed that the gunman fired at his relative over "family reasons" and later shot at others trying to help.

A police spokesman, Bernhard Jens, said earlier the attack “could be a domestic dispute", though at this stage the motive remains unclear.

The suspect was known to have a criminal record, Dutch justice minister Ferd Grapperhaus added.

He warned against early speculation about motives and said "it is important that now the independent investigation will thoroughly go through" the evidence.

Dutch Prime Minister Mark Rutte earlier said the country had been "jolted by an attack" as the official terror threat level - the highest Utrecht has ever seen - was extended until 10pm tonight.

According to local media, the suspect was charged several times over the past years on charges ranging from attempted manslaughter to petty crime in and around Utrecht.

TV channel RTV Utrecht reported he appeared in court exactly a fortnight ago over an alleged rape in 2017.

Police have not commented on any of these alleged crimes.

'CHAOS'

Witness Jimmy de Koster told RTV he was at traffic lights near the square when he saw a person lying on the ground shouting: "I have done nothing".

"I saw a woman lying down, I think she is between 20 and 35 years old," he said.

"At that time I heard 'pang pang pang' three times. Four men walked very fast towards her and they tried to drag her away and then I heard 'pang pang pang' again and those guys let go of that woman again. Very chaos there."

During the suspected attack one woman was seen being "hit in the chest by one of more bullets", while three others were said to have been resuscitated on the tram and in the street, ad.nl reported.

Another witness, Niels, told the Algemeen Dagblad newspaper he believed the gunman had a specific target.

"I had the impression he was firing at one person in particular, because I saw a women crawl out," he said.

"Other people tried to help her, and when they did that he went round behind her and began firing at them.”

Warnings for schools, mosques and indoor public spaces were in place until shortly after 4pm local time.

Mayor Jan van Zanen said that earlier advice to remain indoors was based on fears that shots had been fired at more than one location in the city.

Some local reports suggested there was may have been than one perpetrator but these are yet to be confirmed by police or security forces.

It's not unusual for eyewitnesses to mistake lone wolf gunmen for multiple attackers during the panic of a suspected terror attack.

Police raided a number of properties and arrested two others in connection with the incident, Dutch media reported.

In Utrecht there was a shooting at several locations. A lot is still unclear at this point and local authorities are working hard to establish all the facts. What we already know is that a culprit is at large Netherlands Counter-Terrorism Agency head Pieter-Jaap Aalbersberg

During the lockdown heavily armed guards increased their presence at Amsterdam's Schiphol airport and other transportation hubs as teachers in Utrecht were urged to keep children inside schools with the doors closed for most of the day.

Eerie photos showed whole swathes of Utrecht entirely empty, as citizens of the 350,000 strong city were encouraged to stay inside.

Police reported that a red Renault Clio was stolen in a car-jacking a mile away from the tram shooting just before the alleged attack, and was recovered later on a nearby street.

Later the car was pictured being towed away. It is not yet known if the incidents were connected.

The PM said the alleged attack had left a "mix of disbelief and disgust" throughout the country.

"If it is a terror attack then we have only one answer: our nation, democracy must be stronger that fanaticism and violence," said Mr Rutte.

The shooting comes just days after New Zealand suffered a devastating massacre when a white supremacist gunman stormed two mosques killing 50 people.