DETROIT (Reuters) - One of the busiest border crossings between the United States and Canada, the tunnel connecting Detroit with Windsor, Ontario, was shut down for five hours on Thursday following a bomb threat, but nothing suspicious was found, authorities said.

Detroit police bomb-sniffing dogs explored the nearly mile-long tunnel and gave the all-clear. Travelers were told to use the Ambassador Bridge linking the two countries instead.

Windsor police received a call announcing there was a bomb in the tunnel, prompting an evacuation around midday.

A police forensics team was examining a bank of public telephones in the vicinity of a tunnel entrance where it was believed the call came from, said Sergeant Matthew D'Asti of the Windsor police.

"It was a non-specific bomb threat. It was simply that there was a bomb in the tunnel," D'Asti said. "We have no leads at this time."

Federal, state and city authorities on both the United States and Canadian sides responded, authorities said.

Some 29,000 vehicles travel every day through the tunnel, which passes underneath the Detroit River. The tunnel was completed in 1930 at a cost of $23 million and is jointly owned by the cities of Windsor and Detroit, according to the tunnel authority's website.

Bomb threats against the tunnel have been rare, although one last year also shut it down, Detroit Police spokeswoman Erin Stephens said.

(Reporting By Andrew Stern; editing by Greg McCune and Andre Grenon)