More than half a million primary and kindergarten students in Hong Kong have been ordered to stay home from school for two weeks after a outbreak of the flu.

The school closures, which started Thursday, were ordered after three children died within the last week. The deaths are all suspected to have been caused by the virus.

Hong Kong's top scientists are now studying possible links in the deaths of the children -- a seven-year-old boy and girls ages two and three. Thomas Tsang, controller of Hong Kong's Centre for Health Protection, said two of the three children who died have been confirmed to have the flu.

But World Health Organization spokesman Gregory Hartl said the three deaths weren't directly related to the flu and that two had other illnesses. He said the seven-year-old boy who died Tuesday died of encephalitis.

Nevertheless, Health Secretary York Chow, who announced the school closures late Wednesday, said the action was necessary to contain the flu outbreak, which has affected more than 200 people.

"When children are at school, it's very hard to keep them still and prevent them from contacting each other,'' said Chow. "They may not listen to orders and wear masks or wash their hands.

"We hope such precautionary measures will help reduce the cross-infection of the flu virus in schools and the community," he said.

He added that the schools would be disinfected while they are closed.

CTV's Steve Chao, reporting Thursday from Hong Kong, said many parents only found out about the sudden decision to close schools Thursday morning, as they brought their children to school.

"It sparked a degree of panic as many hospitals as well as doctors' offices soon filled up with parents taking their children who had coughs or a degree of fever in."

Chao said memories of the SARS outbreak in 2003 remain strong in the minds of many in Hong Kong.

"The doctors and the government has come out to reassure the public that they do not believe this recent outbreak is SARS or the bird flu," said Chao.

"They say they believe this is just a higher strain of influenza, a more deadly strain."

Still, Chow said there was no sign of "any significant change of the virus that makes it exceptionally more virulent than the usual flu virus."

In total, the closure will affect nearly 560,000 students at more than 1,700 schools.

With files from The Associated Press