Flat-cap wearing armed robbers staged a brazen daylight raid on an international art fair in the Netherlands Tuesday, smashing a jewellery case with a sledgehammer in front of terrified visitors.

Police said they pulled over a car and arrested two Belgians in their twenties after the four smartly dressed thieves held up the TEFAF (The European Fine Art Fair) in the southern city of Maastricht.

Dramatic social media images showed the robbers threatening people with what appeared to be handguns before running off with an undisclosed amount of what police called "loot".

The venue was evacuated but visitors were eventually let back into the fair, which draws tens of thousands of people over several days. No one was hurt, police said.

"A stall was raided, they fled and we started the search," Wim Coenen, a spokesman for Limburg province police, told AFP. "There were four suspects, two were arrested."

Dutch media said the display case contained diamond jewellery and other items from London jeweller Symbolic and Chase. There was no comment from the firm.

Police confirmed in a statement that "jewellery was stolen. Additional details about the loot are not being provided at this time."

Dutch police launched a huge search involving a helicopter and sniffer dogs and arrested a 22-year-old and a 26-year-old man nearby, both from Belgium, shortly after.

"These two persons were driving a gray vehicle with a Belgian registration number. This car was pulled over... Their possible involvement is still under investigation," it said.

The TEFAF fair is one of the biggest in Europe, and features hundreds of works, including a 17th-century drawing by a Dutch Old Master on sale for one million euros.

Videos on social media showed the four men -- all wearing flat caps, glasses and smart blazers -- amid scenes of chaos at the art fair.

One struck the jewellery case at least 12 times while burglar alarms wailed.

He finally smashed through the glass, reaching in to pick up something before putting it into a bag.

Police said they had arrested two Belgians in their 20s after the raid
Police said they had arrested two Belgians in their 20s after the raid ANP via AFP / Marcel van Hoorn

Two of the men brandished what appeared to be weapons at a bystander, who tried to intervene using a large glass vase full of flowers before backing off.

The men then ran off past a bemused elderly man, who had sat nearby on a bench throughout the drama.

Visitor Jos Stassen told Dutch public broadcaster NOS said he had gone to the exhibition on Tuesday to look at the art in peace.

"I suddenly heard a lot of noise and I turn around and suddenly saw those men," he said.

"One started beating and the others kept people away, scared everyone. I also saw a weapon.

"It went very fast and it lasted a very short time but I'm still shaking a little bit."

The fair's general manager Bart Drenth said the owners of the smashed booth are "very shocked", the Dutch news agency ANP reported.

He said the fair's security protocol worked well despite the fact that the armed robbers were able to walk in, adding: "The police were on the scene within minutes."

A TEFAF spokesman added in a statement to AFP that its "security teams worked quickly to disarm an offender... Nobody was injured during the incident."

The phrase "Peaky Blinders" trended on social media in the Netherlands after the raid because the caps worn by the suspects resemble those in the British crime drama of the same name.

It is not the first time the fair has been targeted by criminals.

A ring and a diamond necklace worth 860,000 euros ($1.2 million at the time) belonging to a London jeweller were stolen at the exhibition in 2011.

The Netherlands has also seen a string of art thefts, with paintings by Van Gogh and Frans Hals taken in burglaries in 2020.