DETROIT (WWJ) –  The international commuter tunnel connecting Detroit with Windsor, Ontario, has reopened after it was shut down for hours due to a bomb threat.

Detroit and Windsor police were called to the scene to investigate after the threat was called in anonymously at around 1 p.m. Thursday.

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Windsor Police Sergeant Matthew D’Asti said someone called in a bomb threat this afternoon from a payphone in Windsor. There was no reason to believe it’s valid. Nonetheless, officials took the threat seriously.

D’Asti said they are working hard now to find the culprit.

“It is our hope that that will be the outcome,” D’Asti told WWJ Newsradio 950. “There are various methods of conducting our investigation and I’m confident that all those areas will be looked at to try to capture the suspect and hold him accountable for his actions.”

D’Asti says the person responsible for the call would be facing several criminal charges including public mischief and threat.

Officials said all vehicles were evacuated from the underwater tunnel stretches about a mile beneath the Detroit River, which is one of North America’s busiest trade crossings.

Initially, traffic going onto plazas on both sides of the tunnel was halted and diverted away from the tunnel. Officials then decided to clear the tunnel and block off entrances and exits on both sides, Brown said.

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Bomb squads from the Detroit and Windsor police departments were called in to help with the investigation. Paramedics and a Detroit Police tactical unit truck was on scene on the Detroit side.

Commuter rush-hour traffic on both sides was redirected to the Ambassador Bridge, which is just west of both downtowns. Cars and buses make up most of the traffic along the 82-year-old tunnel, which was used by about 4.5 million cars in 2011.

The Lodge Freeway was shut down at Larned and Jefferson Avenue through downtown was also closed.  By 4:45 p.m., all streets affected by the threat had reopened to traffic.

“As security concerns were made, customs became a little more thorough at the bridge” said Ambassador Bridge spokesman Mickey Blashfield, Thursday afternoon. “Traffic is up to speed coming into the United States. There is a delay going into Canada. That’s a function of inspections, not border capacity.”

Meantime,  the U.S .Coast Guard was stopping boats and freighters from traveling near the tunnel because of the bomb threat.

“At this point we have an about a thousand-yard safety zone, both north of the tunnel and south of the tunnel,” Coast Guard -Detroit Command Center Supervisor Gabriel Settel told WWJ’s Beth Fisher. “That’s merely to keep the commercial and recreational vessel traffic out of that area.”

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Settel said commercial river traffic was diverted to Belle Isle to anchor until the issue was resolved.