More than 50% of patients being admitted through an emergency assessment unit at Southampton General Hospital are suffering from flu-like illnesses.
In addition, over ten patients are being referred for respiratory examination every day – and 70 to 80% are presenting with influenza, mainly the H1N1 swine flu strain.
Dr Ben Marshall, a respiratory specialist and flu expert, says the "unprecedented" influx has put a major strain on resources as staff across Southampton University Hospitals NHS Trust contend with 100 more patients than expected for this time of year.
"We are seeing a week-on-week increase in patients being admitted with influenza-like illness in Southampton and currently have over 30 adults alone now in hospital receiving treatment – that is unprecedented at this time," he said.
"There is currently lots of seasonal flu around in the community, but what is concerning is that we are taking in many patients under 65 with the H1N1 strain who are also contracting pneumonia, creating further complications."
He added: "While we did expect an increase in flu-related hospital admissions this year, the numbers have been far higher and there is no sign of that letting up any time soon."
Dr Marshall said many people will be able to self-treat at home and advised people, particularly those in at-risk groups such as the elderly or those with chronic illness, as well as pregnant women, to contact their GP and get vaccinated.
He continued: "This situation is likely to continue throughout January as children return to school and adults to work after the festive break, so it would be prudent for those in at-risk groups to have their seasonal flu vaccination as soon as possible."
Meanwhile, three wards at Southampton General Hospital remain temporarily closed to new admissions due to outbreaks of diarrhoea and vomiting – and members of the public are being urged to play their part in helping to beat the bugs.
"We are still managing a very virulent strain of norovirus and other winter sickness bugs, so we would ask for the public's continued support and remind people only to visit hospital if it is absolutely essential," said Judy Gillow, director of nursing at SUHT.
As the New Year weekend approaches, hospital bosses are also asking the local community to try to limit unnecessary attendances at the emergency department.
Dr Michael Marsh, medical director at SUHT, added: "In light of the combination of difficulties we currently face, we would ask anyone concerned about their health to consider the full range of support available to help us manage demand."
A number of options are open to people who are not in need of emergency hospital care, including visiting www.nhsdirect.nhs.uk, telephoning NHS Direct on 0845 4647, visiting a local pharmacy, contacting their GP practice or attending the walk-in centre in Bitterne or the minor injuries unit on the Royal South Hants site.