GO train service has resumed on all lines following the discovery of a suspicious package on the tracks at Exhibition GO Station Wednesday afternoon.

The cylindrical package was spotted by an off-duty police officer sometime after 3 p.m., prompting police to close all four tracks that run through the station.

The CBRN (Chemical, Biological, Radiological and Nuclear) unit was called in to investigate the item, police confirmed.

As a result, service was suspended on the Lakeshore West line between Union Station and Long Branch GO Station.

Riders on the Lakeshore East, Barrie, Kitchener, Milton, Richmond Hill and Stouffville lines were also impacted by the closure, as additional rush hour trains stored at GO Transit's Willowbrook yard in Etobicoke did not have an alternate way to make it to their destinations.

“We’re slowly able to get our trains out of Willowbrook, get them back on all of our lines, and we’ll return service to normal,” Anne Marie Aikins, with Metrolix, told CP24.

“It’s going to take us some time though.”

The package was detonated shortly before 7 p.m. It remains unclear what the package contained, and whether it posed any risk.

Exhibition Station remains closed as police continue to investigate. A second package discovered at the station was ultimately determined to be a child's backpack.

Police expect the station to reopen soon.

“Until police release the scene, we just can’t open it,” Aikins explained of the closure earlier. “We take direction from them, and they are the experts in this, and we’re supporting them as much as we can.”

The closure at Exhibition Station also impacted TTC service with the 509 Harbourfront and 511 Bathurst streetcar routes turning back at Fleet Street instead of travelling on the Exhibition Loop.

Regular service has since resumed.