Chief fire officer Nick Searle said another person had been taken to hospital following the "intense fire which spread very rapidly" in Stone Square at 03:45 BST.
The street was cordoned off by police and fire officers could be seen knocking on the doors of neighbouring homes.
One neighbour said: "I heard shouting in the early hours but I just thought someone was having an argument, then I came downstairs and saw all the fire engines."
Another local resident, who did not want to be named, said: "We all came out on the front and we could see smoke coming over from the houses.
"The sirens woke me up and there were fire engines in the street."
This breaking news story is being updated and more details will be published shortly. Please refresh the page for the fullest version.
You can receive Breaking News on a smartphone or tablet via the BBC News App. You can also follow @BBCBreaking on X, external to get the latest alerts.
