A passenger boat carrying nearly 100 members of a wedding party capsized on Monday in the fast-flowing Indus River in eastern Punjab province.
The incident happened in the Sadiqabad district, about 350 kilometers (210 miles) south of Multan, a main city in Punjab, a senior government official said.
Saleem Assi said at least 64 people, including the bridegroom, were rescued and nearly two dozen people, including children, were still missing.
He said according to their initial information, between 90 to 100 people were on board the boat.
Government and rescue officials said the latest figures showed at least 20 people died in the incident.
Assi said the cause of the accident was not immediately known, but apparently the boat was overcrowded.
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He said all those whose bodies were recovered by the rescuers were women and children.
Such accidents are common in Pakistan, where rickety wooden boats are often used to transport goods and people on rivers and lakes. Most operate without life jackets.