General Motors operations in Windsor, Ont., ended for good Wednesday after a transmission plant closed its doors, leaving 500 workers out of a job.

The closure of the plant, which built transmissions for the Pontiac G5 and the Chevy Cobalt, ended 91 years of the company's operations in the once-thriving automotive town.

Windsor Mayor Eddie Francis said officials are "deeply concerned over the wellbeing" of the newly unemployed workers, but pledged the city will support efforts to retrain and re-employ laid-off GM employees.

"With characteristic Windsor optimism, we look forward to the promise of new opportunities; we regard today's departure of GM as a transition rather than an ending; and we know we can rely on the resilience of our people and their determination to succeed, whatever the circumstances," Francis said in a statement.

Canadian Auto Workers Local 1973 president Bill Reeves said workers have known since May 2008 that the plant would close, but are still upset. GM employed more than 7,000 workers in Windsor at the peak of its operations in the city.

The company has facilities remaining in Oshawa, Ingersoll and St. Catharines, Ont.

GM first arrived in Windsor in 1919, when it opened a branch of its Fisher Body Company of Detroit. Over the years, the company added axle and engine plants, a vehicle assembly facility and the transmission plant. The company "spent billions of dollars and employed thousands of our working men and women," Francis said.

Ontario Premier Dalton McGuinty said Wednesday his government will work with local officials "to find ways to strengthen that economy and create more jobs there."

"The fact that we've known that this has been coming for a couple of years now does not make it any easier for the people who are affected by this," McGuinty said.

With files from The Canadian Press