Police officers were called to Drill Hall in Union Street at 9.15pm last night (Tuesday) to reports of a chemical smell coming from one of the flats.
A spokesperson for West Yorkshire Police said: "Officers and West Yorkshire Fire and Rescue Service attended, and a quantity of chemicals were found which are believed to be used in the production of drugs.
"A number of properties in the vicinity have been evacuated while enquiries continue and a scene remains in place to allow forensic examination to be carried out.
"Anyone with information is asked to contact police on 101, quoting log 2195 of 28/8."
One resident who did not want to be named said: "All I know is there were people dressed a bit like firemen with devices beeping at around midnight coming in and out.
"Then at 1.30am police telling us to evacuate with no explanation other then 'to do with chemicals'.
"The residents were then taken to emergency accommodation by the council.