The blaze at the Love Lei shop in John Street broke out in the ground floor of the building at about 17:00 GMT.
A 48-year-old women was taken to Sunderland Royal Hospital suffering from the effects of smoke inhalation.
The fire service said it still had three appliances at the scene and the road was shut between St Thomas' Street and Bedford Street.
At the height of the blaze the brigade said nine appliances had been used to bring the fire under control.
Leila Chen, 31, who owns the business, said: "A friend phoned me and said my shop was on fire, and I ran down. But we are not allowed in yet.
"I have owned the business since 2010 and this has never happened to me before, so I don't know what to do."
Her father-in-law Tony Swalwell, who owns the building, said: "It seems that the fire was somehow started in the units on the ground floor.
"At about 17:30 we got phone calls about the shop, one was from a lady who was in quite a bit of shock. She was then taken to hospital."
A fire at a bridal shop in Sunderland is believed to have destroyed about 100 dresses.