A gas leak in central Hobart has forced the evacuation of three floors of the Royal Hobart Hospital's Wellington Clinic.

Fire crews arrived at the site this morning after high levels of carbon monoxide were detected.

Police also helped dozens of people evacuate a supermarket, a pharmacy and a pathology clinic.

The clinic building was declared safe about 10:30am.

Hospital spokeswoman Pene Snashell says patients' appointments have been delayed.