Police in Belgium, France and Switzerland have arrested 33 people and recovered "a large quantity" of diamonds and cash in a joint probe into a spectacular $50-million diamond heist at Brussels airport.

The Belgian prosecutor's office Wednesday said a suspected member of the eight-man gang that staged the brazen robbery three months ago had been picked up in France on Tuesday, as Swiss police made eight arrests and seized some of the missing diamonds.

"The probe led to a big police operation yesterday," spokesman Jean-Marc Meilleur told a news conference.

In early morning raids mainly in the Brussels area involving some 200 officers on Wednesday, police made 24 arrests and "recovered big amounts of cash" and luxury cars, Meilleur added.

The February 18 robbery at Zaventem airport at the time was described as "one of the biggest" ever by the Antwerp World Diamond Centre (AWDC), the global dealers' syndicate based in the Belgian port city.

A heavily-armed and hooded gang pulled up in a car on a runway at around 8:00 pm where a Brinks' armoured vehicle had just unloaded Antwerp diamonds into a Swiss passenger aircraft about to take off for Zurich.

In an operation that lasted barely 10 minutes and without a shot fired, the men forced open the hold of the plane and removed some 120 boxes of diamonds.

The gang, posing as police officers, had cut through the airport's perimeter fence and made off with the haul of 50 million dollars (38 million euros) in gems through the same breach.

Meilleur refused to say whether police suspected the gang had worked with insiders at the airport.

The suspect detained in France, 43-year-old Marc Bertolbi, has a lengthy criminal record and Belgium has asked for his extradition, he said.

Bertolbi's lawyer Olivier Rondu later told AFP he "formally denies any role in the heist and impatiently awaits his extradition to Belgium to be heard on the accusations".

Bertolbi owns property in Metz, on the French Riviera, and in Casablanca, Morocco.

In Morocco he runs a restaurant and a luxury car company.

In his car police found 60,000 euros in cash whose origin is so far unknown.

In Geneva, a statement from the Swiss prosecutor's office said police there had seized "a large quantity of diamonds from the spectacular armed robbery in Brussels".

The statement went on to say "a big haul was seized, of 100,000 Swiss francs (80,000 euros) in cash and a large quantity of diamonds, the value of which is currently being estimated".

A businessman and a Geneva lawyer among the eight people being held were facing charges of dealing in stolen goods and obstructing the course of justice, the Swiss statement said.

"The arrests were made thanks to the excellent collaboration between the Brussels and Geneva authorities," it added.

The Belgian authorities said a dozen of the suspects detained in Belgium, aged between 30 and 50, were "well known" to police, some for armed robbery. Some were suspected of receiving stolen goods.

"From the very beginning there's been an intense cooperation between the Swiss, French and Belgian authorities," said Meilleur.

The robbery recalled one in February 2005, when some 75 million euros worth of diamonds and jewels being shipped to Antwerp were stolen in a KLM vehicle at Amsterdam's Schiphol airport.

But the record for a theft of diamonds was in Belgium, in February 2003, when 100 million euros worth of stones were nabbed from the vault of the Antwerp Diamond Centre.

There are more than 4,500 diamond dealers in Antwerp, the hub for a worldwide industry going back at least 500 years, and more than twice as many jobs depend on the trade, the AWDC said.

Eight in 10 of all rough and half of all polished diamonds are traded in Antwerp.