BOGOTA: A boat carrying some 150 tourists on a reservoir in Colombia went down late Sunday night, the air force said.

A statement from the air force said it was not immediately clear if the vessel capsized or sank in the Peñol-Guatapé Reservoir in the north-western tourist town of Guatapé.

An air force helicopter is on its way, the statement added.

The four-deck ship called Almirante went down Sunday afternoon. The reservoir is 68 kilometres from the city of Medellin and one of Antioquia department's main tourist draws.

A video circulating on social media shows the ship going down and dozens of other vessels approaching it to try to rescue people.

"The situation looks serious," said an official with the Antioquia government. Rescued people are being sent to the local hospital in Guatape, the official added.

The town fills with tourists on long weekends like this one, since Monday is a holiday in Colombia.

According to Official Colombia Travel & Tourism's website, the Peñol-Guatapé reservoir is a dam built in the late 1970s that can store water between May and November for use in the summer. Travellers can find a reflecting pool here to fish and ride jet skis and boats.

Medellin's mayor Federico Gutierrez said he is sending a team led by a firefighting crew captain and five scuba divers.

It is not clear at the moment if "there were any casualties, or where the tourists are from", BBC said. However, the publication added that a rescue operation is currently underway.