The famous Edinburgh street was closed as fire services responded to an incident at Debenhams department store.
Police, Ambulance Services and firefighters were called to the store at about 1:20pm on Monday.
Tram services were limited and only ran between Edinburgh Airport and Murrayfield. Lothian buses said their services were also diverted due to the closure of Princes Street between Castle Street and South Charlotte Street.
Fire crews have also been spotted in nearby Rose Street and Frederick Street and a police cordon has been put across Castle Street.
A Scottish Fire and Rescue Service spokesperson said: “We were alerted at 1.23pm today, Monday, April 19, to reports of a fire in the ground floor of Debenhams on Princes Street Edinburgh.
“Operations control immediately mobilised four fire engines and an aerial appliance to the scene.
“Crews wearing breathing apparatus entered the building where the fire was found to be within the ground and lower ground floor and a further four appliances were mobilised.
“No casualties have been reported and firefighters continue to tackle the fire.”
The fire was found on the ground and lower ground floors, to which a further four appliances were dispatched with more than 30 firefighters on scene.
Eye-witnesses said that workers from nearby buildings such as boots had to evacuate customers and staff.
The street reopened at 17:20pm after firefighters had tackled the blaze and left the scene.
Bus services have resumed as normal and full tram services are expected to start again soon.