Shoaib Sadiqui, administrator of Karachi, the country's largest city, said the victims ignored safety warnings.
He said a large number of people had gathered on the beaches to celebrate Eid, the holiday marking the end of Ramadan.
Farooq Baluch, director of Pakistan's largest private emergency service, said rescuers had recovered 19 bodies from the water near the southern city.
Mr Sadiqui said rescuers from the Pakistani navy and Baluch's Edhi Foundation were still searching the waters for missing people.
He added: "This is a very sad incident and we are using all of our resources to trace and rescue some of the remaining missing people."
Crying relatives of the dead and missing gathered on the beach.