Pressure is growing on hospital services across Yorkshire and Lincolnshire, with figures showing thousands of staff have had to take time off due to Covid-19.
A critical incident has been declared at the United Lincolnshire Hospitals NHS Trust, where bosses said the situation was causing "extreme and unprecedented" shortages due to workers having to self-isolate.
It is one of at least seven trusts to have declared critical incidents as the Omicron variant causes cases to surge.
The latest figures, from Boxing Day, show that major staff absences are being experienced at many of the region's hospitals:
Leeds Teaching Hospitals Trust - 1407 off, 502 due to Covid (35%)
Sheffield Teaching Hospitals NHS Foundation Trust - 2093 off, 1144 due to Covid (54%)
Bradford Teaching Hospitals NHS Foundation Trust - 504 off, 116 due to Covid (23%)
Hull University Teaching Hospitals NHS Trust - 605 off, 265 due to Covid (43%)
United Lincolnshire Hospitals NHS Trust - 643 off, 150 due to Covid (23%)
Leeds Teaching Hospitals NHS Trust said it was working to minimise the impact on patients.
In Bradford, people are being asked only to attend accident and emergency if they have a genuine need.
Boris Johnson has asked ministers to develop "robust contingency plans" for staff absences, as the government acknowledged the high Covid levels could hit businesses hard.
It comes amid reports that work-from-home guidance in England could be set to roll on for most of January.