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.”
It is understood the area around the McDonald’s restaurant will remain closed for the rest of the day.