A McDonald’s restaurant has been closed with police currently stationed outside the site.
A notice displayed outside the building at Brighton Marina warns customers that “unfortunately this store is closed today”.
Two police cars are parked outside the restaurant and passers-by said areas inside the store have been “taped off”.
In a post on social media, another visitor to Brighton Marina said there were “police and ambulances all over” the site shortly after 12.30pm.
A Sussex Police spokeswoman said: “Emergency services were called to McDonalds restaurant at Brighton Marina at 12.05pm on Wednesday, April 14, after a man was found in distress on the premises.
“The man was taken to hospital by ambulance.”