Surgeries and other medical procedures are being put off, as a strike causes major disruption in Christchurch.

Almost 150 medical imaging technologists who are part of the Apex Union and work for the Canterbury District Health Board are walking off the job this morning for 24 hours and again on Wednesday.

CDHB chief medical officer doctor Sue Nightingale says the impacts of that are huge.

"For surgery, we need a certain number of surgeons on one day, which is quite difficult to arrange.

"So if that gets deferred, its not something which can be done the next day or even the next week."

Emergency procedures are still going ahead.