The Royal Victoria Hospital is one of those under pressure.
Two health trusts in Northern Ireland have said they are under “extreme” pressure this weekend.
It comes after last weekend when the ambulance service experienced lengthy delays outside emergency departments and hundreds of patients were left waiting on beds.
The latest data available shows that from midnight on January 1 to midnight on January 2, there were 1348 attendees at NI emergency departments, with 406 patients waiting on a hospital bed.
Now, on Saturday, the Belfast Trust said: “Our Adult Emergency Departments at the RVH and Mater are under extreme pressure.
“Anyone attending with a non-urgent condition will have a very long wait to be seen.
“Please only attend if your condition is life threatening, urgent or needs immediate attention.”
We need your consent to load this Social Media content. We use a number of different Social Media outlets to manage extra content that can set cookies on your device and collect data about your activity.
Please review your details and accept them to load the content
The Western Trust has also said: “Altnagelvin Emergency Department remains extremely busy this morning with 84 people in ED and 68 awaiting admission.
“For less urgent matters, please use the Phone First service on 0300 020 6000 who will advise on the best place for you to attend for your condition.”
On Friday health minister Mike Nesbitt and community minister Gordon Lyons released a joint statement urging the public to access advice and services that can help them to keep warm and keep well.
NI is currently bracing for snow and ice in the coming days.
Mr Nesbitt said: “Winter can affect people’s health, particularly those over 65 and people who have long-term health conditions.
“Keeping warm, seeking early treatment for minor illness and keeping in contact with others are important ways of ensuring you stay as physically and mentally well as you can over the colder months.
“Your local pharmacist can provide help and advice, particularly for coughs and colds. They can also provide prescriptions for treatment of some minor illness, such as sore throats, without the need to wait for a GP appointment.”