Locals present on the scene have spotted armed police and fire crews present at Southmead hospital in North Bristol.
Uncomfirmed reports suggest the evacuation may be the result of a bomb threat.
North Bristol NHS tweeted: “We are currently responding to a security incident in our Emergency Department.
“We’re asking all members of the public to please stay away from the Emergency Department at Southmead Hospital whilst this incident is ongoing.
“This means that we have had to cancel all outpatient appointments and visiting today.
“We are unable to comment further at this time but will issue updates as soon as possible.”
We will keep this story updated as more details emerge.