Ontario residents seeking the H1N1 vaccine were urged Thursday to let those in high-risk groups go first, as high demand for the vaccine threatened to swamp clinics in Toronto and elsewhere.

The overwhelming demand for shots had thousands of people lining up Thursday at two clinics in Toronto. Overwhelming crowds and the resulting traffic problems even forced road closures near a clinic west of the city.

“There will be enough vaccine in Ontario for everyone who wants and needs a vaccine,” said Deb Matt­hews, minister of health and long-term care.

But with only the two locations operating in Toronto, people turned up as early as 6 a.m. and many decried what they called a lack of organization.

By early afternoon, both Toronto clinics — originally intended for health-care workers and high-priority groups — were turning away newcomers but said people already in line would get their shots.