More than 1.1 million people in Britain have succumbed to the norovirus winter vomiting disease so far this season, and health officials expect cases to jump higher after a Christmas and New Year dip.

Britain's Health Protection Agency (HPA) said cases of highly contagious norovirus have risen earlier than expected this winter - a trend that has also been seen across Europe, Japan and other parts of the world.

Health officials in the United States said last week that more than 400 people on two cruise ships had been taken ill with a sickness suspected of being due to the norovirus, and hospital wards and nursing care homes in Europe have been forced to close to try to stop infections spreading.

Norovirus is transmitted by contact with infected people or contaminated surfaces, food or water.

HPA data released on Wednesday showed there have been 3,877 laboratory-confirmed cases of norovirus in Britain this winter, 72 percent higher than the number of cases reported at the same point last year. The reason for the rise in not known.

For every laboratory-confirmed case, scientists estimate some 288 unreported cases, as the vast majority of those affected don't go to a doctor. This means the number of people affected in the UK so far is likely to be more than 1.1 million.

"As we have seen in previous years, there has been a dip in the number of confirmed laboratory reports owing to the Christmas and New Year period," said John Harris, the HPA's norovirus expert.

But he added that the HPA expected to see a rise in the number of laboratory reports in the next few weeks.

Norovirus symptoms include a sudden onset of vomiting, which can be projectile, and diarrhea, which may be profuse and watery. Some victims also suffer fevers, headaches and stomach cramps.

"If you think you may have the illness then it is important to maintain good hand hygiene to help prevent it spreading," said Harris. "We also advise that people stay away from hospitals, schools and care homes as these environments are particularly prone to outbreaks."