Police and medics in Pakistan say 40 people have died as a result of drinking contaminated alcohol in the city of Karachi.

Doctors were trying to save about two dozen others admitted to hospitals in the southern port city where scores fell sick on Thursday and Friday (local time) after drinking the liquor, medics said.

"So far 40 people have died because of drinking toxic liquor," city police chief Javed Bokhari said. About 14 died on Thursday and another 13 on Friday.

"It is tragic to see people dying in so many numbers," said Dr Seemi Jamali of Jinnah Postgraduate Medical Centre, where many of the victims were admitted.

"The victims suffered irreversible damage because of poisoning."

Many victims were shy of reporting to hospital because the holy month of Ramadan is being observed in this overwhelmingly Muslim country.

Drinking alcohol is prohibited in Islam but even those who drink often stop during Ramadan.