(CNN) -- The major tunnel between Windsor, Ontario, and Detroit was scheduled to reopen at 5 p.m. ET Thursday following a shutdown because of a bomb threat, Windsor police said.
Police "fully inspected" the tunnel before reopening it, Windsor authorities said.
The bomb threat led to traffic backups as drivers on both sides of the border were rerouted.
Employees at the Detroit-Windsor Tunnel received an anonymous phone call around 12:30 p.m. from someone saying there was a bomb in the tunnel, Sgt. Matthew D'Asti with Windsor police told HLN.
Authorities were working together on both sides of the border to investigate and search the tunnel for any possible device, D'Asti said.
Neal Belitsky, president and CEO of Detroit-Windsor Tunnel, said the threat was called in to the Canadian side.
Authorities treated the matter "as a nonspecific, anonymous bomb threat," said D'Asti. The tunnel was evacuated.
The tunnel is one of two international crossings between the cities of Windsor and Detroit.
Traffic was being routed to the other, a bridge about two miles away.
Approximately 27,000 to 29,000 vehicles pass daily through the tunnel, which opened in 1930.
The Coast Guard said it set up a safety zone in the Detroit River in order to keep vessels away from the tunnel.
CNN's Chandler Friedman, Devon Sayers and Michael Martinez contributed to this report.