DETROIT -- Although state police say that no specific terrorist threats have been directed at Michigan, agents at the Detroit-Windsor border are on heightened alert Wednesday, Local 4 reported.

Authorities have been reacting to President George W. Bush's announcement earlier in the day that he raised the nation's terror alert warning level to Code Orange. Code Orange is the second-highest alert level and indicates there is a "high risk" of attack on Sept. 11.

A slight backup was apparent at the border early Tuesday evening, as agents checked vehicles coming into the country. Wait times were reportedly five to 10 minutes.

State Police Col. Stephen Madden said all local law enforcement agencies were notified of the increased threat level and asked to review security at bridges and other critical infrastructures, including the Soo Locks and water and electric facilities.

"The public should rest assured that we are taking reasonable and prudent steps based on the increased threat level but, at the same time, we are cautioning everyone not to overreact to the information," Madden said. "Michigan's public safety community is prepared to respond to any situation."

FBI spokeswoman Dawn Clenney said that motorists will notice the presence of more officers at least until the alert has been downgraded.

Border officials are planning a tribute to the victims and survivors of last year's attacks on Wednesday.

The Ambassador Bridge and Detroit-Windsor Tunnel will close to observe a moment of silence beginning at 9 a.m. The two river crossings between Detroit and Windsor, Ontario, will close for three minutes.

Officials with the privately owned tunnel and bridge say the moment of silence will serve as a time for remembrance and reflection.

Detroit is the largest city on the United States-Canadian border. The Ambassador Bridge is the busiest crossing between the two countries.

The tunnel opened in 1930, and is jointly owned by the cities of Windsor and Detroit, and operated by the Detroit-Windsor Tunnel Corp.

The Ambassador Bridge is privately owned. It is one of the busiest border crossings in North America. More than 10 million vehicles cross the bridge each year, according to bridge officials.

Gov. John Engler was notified of the code change early in the day during a conference call with other governors, his spokeswoman, Susan Shafer said. He was in close contact with state police throughout the day, she said.

The level had been at yellow, in the middle of the five-color scale. The highest level is red, for a severe alert.

Code Orange calls for government officials to take extra precaution at public events, including moving or canceling them if necessary.