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GUATAPE, Colombia (Reuters) - Rescue workers searched on Monday for two people missing after a tourist boat sank in a reservoir in north-central Colombia, killing seven.

The cause of the accident on Sunday was still unclear, officials said. Use of the Penol-Guatape reservoir, a popular site for water sports and tours, was restricted as the search continued.

Reports of the dead and missing have varied widely since the accident, as have figures for how many people were onboard the boat.

“The official figures at this hour are two missing, seven dead and 158 rescued,” the national disaster relief agency said on Twitter. “Operations continue.”

Officials initially reported nine people dead and 28 missing, figures which later dropped to six and 16 respectively. Some survivors rescued by private boats were taken to different docks on the reservoir shore and so were not immediately accounted for, authorities said.

Videos posted on social media showed motorboats coming to the aid of passengers on the upper decks as the boat rocked from side to side. Survivors told local television they heard a loud noise before the boat began to sink.

It is a long holiday weekend in the Andean country and the reservoir is a well-known destination for families.

Officials were interviewing the captain and investigating allegations by some passengers that they did not have life-jackets, Vice Transport Minister Alejandro Maya told journalists at the scene earlier on Monday.

President Juan Manuel Santos visited rescue crews at the reservoir, about an hour’s drive from the city of Medellin, on Sunday night.