VANCOUVER - A potentially explosive situation has been hidden for decades under one of the most popular gathering places in Vancouver's Stanley Park.

Police say an ancient military mortar shell was discovered by a man using a metal detector in the area of Brockton Oval, where a variety of sports teams gather to play.

Investigators are now digging into the mystery of how the post-Second World War device came to be buried under ground frequently passed over by athletes, joggers and picnicking families.

"It was off in the bushes ... but the public did have access to it," said Vancouver police Sgt. Randy Fincham. "Presumably they've been walking over it or walking in the area of it for 50 or 60 years."

The projectile was found tail-up, rusty and coated in dirt on Thursday by the man who started shovelling between the area of Brockton Oval and Deadman's Island, which houses the HMCS Discovery naval base.

He had partly unearthed the device when he realized it could be dangerous and called police.

Technicians cordoned off the area and the eight by 35 centimetre mortar was carefully deposited in an explosive containment unit for transport out of the park.

They'll investigate whether the device is linked to the reserve base, which was established on the island jutting out from the park in 1943.

"Presumably it fell off a truck, it got buried in the ground, it got dropped by somebody. During those days it was a lot less populated than it is now," Fincham said. "(I'm) not saying it's their device, that would be a logical thing for us to look at."

Technicians will take the shell to a rock quarry outside the city where they'll use a small explosion to ensure it's inert. Then they'll examine the pieces for signs it had an explosive charge.

Police have taken photographs and searched the Internet to find comparable images in the early stages of their historical analysis. They will attempt to date the device and determine its origins, but Fincham said the remaining fragments won't be "the museum quality that they were before."

He advised the public against relic hunting in the park.

"There certainly is the potential that there are more of them," he said. "Before yesterday, I would have said that it's highly unlikely that (there) would be any in the park."

News from © The Canadian Press, 2014