Six hospitals in the region have issued a joint warning for people to stay away from emergency departments except for in "genuine, life-threatening situations", after a surge in numbers left some patients waiting for up to 12 hours.
Hospital trusts across West Yorkshire and Harrogate said the current pressures have left them with no choice but to prioritise patients presenting with acute illness or injuries.
West Yorkshire Association of Acute Trusts (WYAAT) said its most recent emergency department figures show a 14.2% increase in attendance compared with the same week last year.
Dr Andrew Lockey, emergency medicine consultant with Calderdale and Huddersfield NHS Foundation Trust, said: "It's really important that people only come to an accident and emergency department if they really need to.
"Our hospitals are extremely busy, and people are having to wait a long time to be seen.
"Over the past two weeks we've faced huge challenges with the sharp uplift in the number of people attending accident and emergency. This places additional pressure on our teams who are responsible for treating patients with serious and life-threatening conditions.
"If you are unwell and are unsure which healthcare service you need, call NHS 111. A highly trained clinical adviser will direct you to the most appropriate service."