General Motors closed its only remaining manufacturing plant in Windsor, Ont., on Wednesday, ending a 90-year relationship with the border-city.

The closure of the transmission plant puts about 500 employees out of work.

Windsor Mayor Eddie Francis said city officials are "deeply concerned" about the GM workers. The city will continue diversification programs and support efforts to retrain and re-employ the workers, he said.

"It was tough coming out, saying goodbye to some close friends," said Mark Mitchell, who worked at the plant for 29 years. "It was rough."

"It's a sad time … a lot of good people are going to be losing their jobs," said machine operator Duncan St. Amour, choking back tears as he spoke with CBC News.

St. Amour was 19 years old when he won a job lottery for a position at GM.

Thirty years later, St. Amour said, his life is about to change but he is trying to stay positive.

"Yesterday I joined a gym," he said. "I bought a bike, and now, I'm going to look for another job."

St. Amour said the mood inside the plant Wednesday was sombre, with a lot of handshaking and group hugs. He said he had thought long and hard about his last day at GM and about what his last action would be.

"Thirty years ago, I walked up the stairs to go have our group orientation. Today, I'm going to walk down those same steps and hold my head up high."

GM was once one of the biggest employers in the city, with more than 7,000 workers. Its presence dwindled over the years to just one plant, and in May 2008, the company eliminated 1,400 jobs and announced it would close the transmission plant by the end of this month.

"Everything I have is because of General Motors," Dennis Beaumier, a 30-year veteran at the plant, said. "General Motors has been good to me."

In turn, GM workers have been good for Windsor, raising millions of dollars for charity, even during hard economic times. In November 2009, even after they knew their plant would be closing, workers raised $160,000 for the local United Way — 15 per cent more than what they raised in 2008.

"I think there was a time when we couldn't have imagined that we would not have a GM presence," said Sheila Wisdom, the United Way's executive director.

GM still operates three other plants in Ontario — in Ingersoll, St. Catharines and Oshawa.

CAW president Ken Lewenza has said he expects the company to make new investments in Windsor if it shows growth or profit.

With files from The Canadian Press