The accident sparked an outpouring of grief among residents who only recently resumed festivities on the banks of the Tigris after the northern city's recapture from the Islamic State group.

The vessel was packed with men, women and children crossing the Tigris to go to a popular picnic area.

"It's a disaster, no one expected that," said a young man who had just managed to reached the shore.

"There were a lot of people on the boat, especially women and children," he told AFP.

Seventy-one people died including 19 children, according to interior ministry spokesman Saad Maan, while 55 people were rescued.

"The boat sank because there were too many passengers on board, more than a hundred," another security official based in Mosul told AFP.

The authorities had warned people to be careful after several days of heavy rains led to water being released through the Mosul dam, causing the river level to rise.

Hundreds of people who had flocked to the forested area for the first days of spring gathered on the river banks as the disaster unfolded.

Ambulances and police vehicles transported the dead and wounded to hospitals in the city of nearly two million people.

IS turned Mosul into their de-facto Iraqi capital after the jihadists swept across much of the country's north.

The city spent three years under the group's iron-fisted rule until it was recaptured by Iraqi troops backed by a US-led coalition in 2017.

Iraq's last major boat disaster was in March 2013 when a floating restaurant sank in Baghdad, killing five people.

Prime Minister Adel Abdel Mahdi put health services on alert and instructed all available teams to mobilise to find survivors after Thursday's accident.

He ordered an investigation "to determine responsibilities".