Giant cranes were on the site today as hospital bosses sought to ensure maximum safety,
A spokesman at Royal Preston said: "High winds appear to have damaged one of the chimneys at the hospital and investigations have been going on today and will be continuing over the weekend to assess the extent of the damage.
"In the meantime we have had to move some staff out of offices in the vicinity as a precaution. It has not affected any wards or other patient areas.
"We have placed an exclusion cordon around the site while the work goes on. Two cranes have been brought in so the chimney can be examined safely.
"The area is adjacent to staff car park E."
Workmen needed to remove cladding on the chimney to examine the structure properly.