The bug is known as a small round structured virus
Two Glasgow hospitals have been forced to close their doors to new admissions.
The Public Health Laboratory Service said the virus was common, but levels were higher than usual this year.
Heath Secretary Alan Milburn said he was "keeping a close eye" on developments.
He said: "It's right to be concerned about it.
"It happens every year but the important thing is that we keep it under close monitoring, which is precisely what we are doing."
Schools appear to be particularly vulnerable. Thousands of children in the north-west of England have fallen ill.
Three hundred of the 900 pupils at All Hallows School in Penwortham are currently off sick.
Victim
She said: "You feel terrible really for about three days. All my friends have come down with it, and there is a lot off school."
The sickness is often known as "winter vomiting disease".
It is caused by bugs known as small round structured viruses and is highly contagious.
The illness usually starts with the sudden onset of severe and dramatic vomiting.
The victim can be absolutely fine one minute and then vomiting the next. Some people develop diarrhoea.
Symptoms usually last for 24-36 hours, and there are rarely any long-term effects
Professor Hugh Pennington, an expert in disease from Aberdeen University, described the bug as the "Mike Tyson" of viruses.
"It is a very clever virus. It is pretty good at spreading itself."
Biggest outbreak
Fifteen hospitals across Scotland are now known to have been affected by the virus.
The most serious outbreak so far has occurred at the Victoria Infirmary in Glasgow, which put a block on all new admissions on Monday.
By Wednesday evening a total 295 patients and staff had become infected.
Health chiefs say they hopes to resume normal patient admissions on Sunday.
The North Glasgow University Hospital Trust announced on Tuesday that no new patients would be admitted to the Drumchapel Hospital for at least 24 hours after 11 people there developed the sickness.
In Wales, two dozen staff and elderly patients on a care ward at Morriston Hospital in Swansea were reported to have been struck down by the virus on Thursday.
Health chiefs closed the ward to new admissions until the outbreak clears.