Visiting at one hospital has been cut as health boards across Wales have reported increases in people with flu.
Officials said they wanted to reduce the risk of spreading the illness at Wrexham Maelor Hospital so they had cut all but essential visits to the site.
Hospitals in south Wales said they were operating under “extreme pressure” with increases in flu and sickness cases.
Public Health Wales said the rise in flu cases was due to several strains, including one that affected Australia.
The latest published health report for the week before Christmas showed a Wales-wide increase for flu to 13.7 consultations per 100,000.
This compared with 8.7 consultations per 100,000 in the week before, and pushes the number of cases above levels normally expected for this time of year.
- A sudden fever – a temperature of 38C or above
- Aching body
- Feeling tired or exhausted
- Dry, chesty cough
- Sore throat
- Difficulty sleeping
- Diarrhoea or tummy pain
- Nausea and being sick
SOURCE: NHS Choices
A Betsi Cadwaladr University Health Board spokesman said: “We are asking the public to help us prevent flu spreading and only essential visits will be allowed at Wrexham Maelor Hospital at this time.
“Visitors to all of our hospitals should follow any advice notices and guidance both for their own protection and to help prevent the spread of infection.
“Flu is circulating in communities throughout north Wales and this action will help us reduce the spread of infection and keep our patients and staff safe this winter.”
A Cardiff and Vale University Health Board spokesman said: “We have seen an increase in patients presenting with flu and other respiratory conditions, together with a number of patients experiencing gastrointestinal problems, including norovirus.
“A small number of hospital beds have been closed to admission as a precaution.”
Aneurin Bevan University Health Board (ABUHB) said both the Royal Gwent Hospital in Newport and Abergavenny’s Nevill Hall “remain under a great deal of pressure”.
Officials said the two hospitals had been dealing with “an unusually high intake of very poorly people, particularly with clinically significant respiratory illnesses”.
Health boards operate at four levels to determine workload and emergency pressures with level one the lowest and level four the highest which is regarded as “extreme pressure”. ABUHB said it was operating at level four.
Abertawe Bro Morgannwg University Health Board said it had seen patients seriously ill with flu admitted to its hospitals and was also seeing more cases of sickness bugs.
It advised people with less urgent conditions to use other services such as Neath Port Talbot Hospital minor injury unit, GP surgeries and pharmacies.
Dr Richard Roberts from Public Health Wales said: “The flu vaccine remains available and we would strongly advise that those aged 65 years and over, between six months and 65 years in risk groups and pregnant women who have not had their flu vaccine this winter, to make sure they don’t miss out and speak to their GP surgery or community pharmacy as soon as a possible.”