SAINT JOHN, N.B. -- Jewellers across the country are being warned to check their stock for fake diamonds after a Toronto-area couple were charged in a daring diamond switch that could be connected to a string of similar heists nationwide.

Police in Saint John, N.B., said Grigori Zaharov, 70, and Natalia Feldman, 44, of Vaughan, Ont., were arrested overnight Thursday outside a condo tower in Vaughan.

The pair was sought in an Oct. 7 theft at W. Smith and Co. Fine Jewellers in Saint John. Store owner Wayne Smith said the thieves presented themselves as a couple arguing over how many carats to buy, and then switched a $10,000 diamond with a fake while the salesperson was distracted.

The Saint John force said the couple "are suspects in numerous other jurisdictions for similar incidents," and multiple police agencies are working "to determine the entirety of their actions."

"The same two suspects appear to have been involved in a similar theft in Charlottetown and we also received information that a similar theft had taken place at a jewellery store in Fredericton," said Saint John police Sgt. Chuck Breen.

"They were travelling and obviously they are professionals. They're quite good at what they do."

John Lamont, director of loss prevention for Jewellers Vigilance Canada, said there have been reports of at least five similar incidents from coast to coast. But because of the nature of the heists, there are likely many other victims who aren't even aware of it yet, he said.

"The fact that they have been seen from Vancouver all the way over to the East Coast would indicate they made a lot of stops on the way, and I think there's a lot of jewellers out there that might not even know they've been hit," said Lamont.

"We're asking our network of jewellers to check their diamonds to make sure they haven't been victimized."

Smith went public about the robbery at his store this month, and said he has since heard directly from stores and police officers across Canada about similar heists. Smith estimates more than $1 million in diamonds may have been stolen by the pair.

"It's going to get much bigger," he said in a phone interview Thursday, adding that he high-fived and hugged staff members after hearing of the arrests.

Smith said he was thrilled the sophisticated camera system at his store played a major role in identifying the suspects.

"A good old little Saint John store was responsible for bringing down, it looks like, a major theft ring," said Smith.

Breen said there's no doubt Smith's camera security system played a big part in the arrests.

"It's a phenomenal set-up. The pixels from the freeze frames -- I've yet to see a video surveillance from any businesses we've dealt with as good as the one Mr. Smith has," said Breen.

Breen said the pair are being held by the York Regional Police Service and will be returned to New Brunswick to answer to the charges, likely within the next few days.

Smith said he has more than 40 years experience in the jewelry industry and the employee who dealt with the suspects followed the store's policies.

"The frustrating part is you put camera systems in and we have all these rules and regulations and it just shows that people can try and find ways to beat it," said Smith.

Lamont said there are roughly half a dozen larger jewelry heists in Canada every year.

He said a good way for jewelry stores to avoid being victimized by this particular scheme is to check loose diamonds both before and after they are handled by a customer.

-- By Aly Thomson in Halifax.