Thousands of workers at General Motors automobile plants in the United States are on strike, as negotiators continue to try to reach agreement on health insurance payments and other issues.

Some of the United Auto Worker union's 73,000 GM employees left work and began picketing Monday morning after a union deadline for an agreement expired.

In the first strike action at GM by the United Auto Workers since 1998, several U.S. plants were closed and at least one factory in Canada. Union officials say more factories in Canada and Mexico may have to halt work in the coming days.

News reports say negotiators continue to discuss plans for a company-supported health care trust fund. Union leaders are also seeking guarantees that GM will keep production jobs in the United States.

The union's contract with GM expired on September 14, but union members stayed on the job while negotiations were underway.

Some information for this report was provided by AFP and Reuters.