The community is being urged to support local hospitals during a period of "heavy demand."
Dr Peter Williams, the medical director of Mersey and West Lancashire Teaching Hospitals NHS Trust, is calling for people to help staff by avoiding unnecessary visits to Whiston Hospital's A&E department.
He said: "People will have seen the pressure the NHS has been under both locally and nationally over the past few weeks.
"It is no different here and it has been extremely busy at all our sites with huge demand on our emergency services with an increasing number of people with flu and respiratory illnesses coming to hospital."
Dr Williams wants to make sure everyone gets the best care possible at all times, and it is still "really important for people with urgent and emergency health conditions to still come to A&E if they need to."
He added: "That will always be our advice.
"But we would ask anyone with non-urgent conditions to look at alternative services such as 111 online, your local GP, pharmacy or walk-in centre in the first instance, to see if you can get help."
Dr Williams assured people that staff are working "incredibly hard" to deliver the best care possible for each patient.
However, he warned that if your condition isn't urgent, there may be a longer wait for treatment while they treat the sickest patients.
He concluded: "It's really important that everyone gets the care that they need, and I would like to thank everyone for their co-operation, which is really appreciated."