Public health units in Ontario will open more clinics and expand operating hours next week in response to overwhelming demand for the flu shot that is forcing some clinics to turn people away.

Dr. Arlene King, the province' chief medical officer of health, announced the changes on Thursday as clinics across the province scramble to keep pace with the number of people lining up for the H1N1 pandemic vaccine. Toronto Public Health closed one of its clinics to new arrivals less than an hour after opening on Thursday when the lineup swelled to more than 1,000 people.

Demand for the vaccine is far exceeding expectations, Health Minister Deb Matthews said on Thursday at a hurriedly-called news conference with Dr. King.

"We are responding as quickly as we can to the higher than expected demand," Ms. Matthews said.

Health officials have spent years planning for the next pandemic. But now that it has arrived, the unprecedented demand for the vaccine is forcing them to revise their plans almost daily.

Ms. Matthews said that just a few days ago, health officials were concerned that not enough people would heed their advice to get the flu shot.

"Now it looks like there will be significant uptake," she said.

Fears about the H1N1 virus, which increased dramatically this week following the tragic death of a previously healthy 13-year-old boy from the disease, are also creating other strains on the health-care system, with many hospital emergency rooms inundated with worried parents and the province's Telehealth phone lines swamped with callers.

The volume of calls to Telehealth is five times higher than expected, Ms. Matthews said.

Health officials are pleading with the public not to jump the queue and to let those who are most at risk of developing complications from the flu get their shots first.

Progressive Conservative health critic Christine Elliott called on the government earlier this week to operate the immunization clinics around the clock.

"The H1N1 virus is not keeping 9-to-5 hours, and neither should we," she told reporters. "No bureaucratic excuse justifies forcing families to wait hours or days before obtaining a potentially life saving vaccination."

Ms. Elliott also said the government needs to make it as easy as possible for people to get the vaccine by opening clinics in office buildings and schools.

New Democrat Leader Andrea Horwath accused the government of dropping the ball in its response to the H1N1 virus.

"The government had many, many months to plan for this pandemic and the rollout of the vaccination, and they did a dismal job" she told reporters on Thursday.