Police in Canada are investigating a daring heist involving nearly CAD20 million (US$14.8 million) in gold and other "high value" items at Toronto's Pearson International Airport.

Peel Regional Police said on Thursday evening that the gold and other items were stolen on Monday after containers were unloaded from an aircraft. “An aircraft arrived here at the airport in the early evening. As per normal procedure, the aircraft was unloaded and cargo was transported from the aircraft to a holding cargo facility,” inspector Stephen Duivesteyn said while announcing the theft.

"What I can say is that the container [had] a high-value shipment. It did contain gold but was not exclusive to gold and contained other items of monetary value."

The Royal Canadian Mounted Police were also investigating the theft, which was one of the largest in Canadian history. The Greater Toronto Airports Authority declined to comment, citing an "active police investigation."

Northern Ontario goldmines frequently ship bullion through the city's airport, which handles nearly half of the country's air cargo.

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Duivesteyn refused to call it a "professional" job at this time, saying the investigation was ongoing and that the incident was isolated. The intended destination of the stolen cargo was not identified by police, nor was the gold confirmed to be still in the country. “This is very rare,” Duivesteyn said. However, this isn’t the first time a Toronto-area airport has made headlines for a gold heist.

On September 25, 1952, $215,000 in gold bullion was stolen from Malton Airport, the predecessor to Pearson. It was the largest gold robbery in Canadian history at the time. In today's dollars, the theft would be worth $2.3 million.

Six wooden boxes of gold were stolen from a steel cage in the airport's cargo area before being loaded onto a plane bound for Montreal during the heist. “It just seemed to vanish,” one investigator told the Toronto Star at the time. The seemingly perfect crime, with no witnesses, was never solved.

Trans-Canada Air Lines was renamed Air Canada in 1965, the same airline that is suspected of being the victim of Monday's theft.

Previous high-value heists have targeted a priceless photograph as well as the country's vast maple syrup stash. Richard Vallières, the mastermind, stole $17 million in syrup from a Quebec warehouse in 2014, part of the province's strategic reserve. 

The heist spawned both a wide-ranging investigation - which eventually led to his capture - and a Hollywood screenplay.