Two primary schools have been forced to shut after pupils and staff were taken ill with suspected norovirus.
St Mary's Catholic Primary School in Jarrow, South Tyneside, and St Mark's Church of England School in Stockton, on Teesside, are shut for a second day.
Hundreds of staff and pupils were struck down with vomiting and diarrhoea and they have shut to undergo a "deep clean".
Statements released by the schools said they would re-open on Monday.
A spokesman for Public Health England said: "Anyone that has diarrhoea and vomiting should stay away from work or school until they have been free of symptoms for 48 hours.
"Everyone should be encouraged to practice good hand hygiene and wash hands thoroughly and regularly at all times, but particularly after using the toilet and before eating."
Sometimes known as "winter vomiting viruses" noroviruses are the most common cause of stomach bugs in the UK, affecting all ages.
It is estimated that between 600,000 and a million people in the UK become infected each year.
About 12 to 48 hours after becoming infected, the virus causes sudden onset of nausea followed by vomiting and diarrhoea.
The illness is not generally dangerous and most people make a full recovery within one to two days.