At least nine people are dead and dozens are missing after a tourist boat carrying about 150 people sank near a popular sight-seeing destination in Colombia.

A major rescue operation is underway at a reservoir in Guatapé near the capital Medellin, with the air force saying on Twitter that it had dispatched a helicopter and divers to the scene.

Witnesses captured footage of the multi-story ferry rocking back and forth as it began sinking, as a fleet of recreational boats rushed to the scene to rescue tourists from the ship.

Survivors have reported that none of the passengers on board were wearing life jackets.

Video shows the moment "El Almirante" sank in #Guatapé. Mayor of nearby #Medellin sent divers and more rescue teams pic.twitter.com/dVYPTXh7OE

— Benjamin Alvarez (@BenjAlvarez1) June 25, 2017

Medellin’s mayor Federico Gutierrez said firefighters and scuba divers were en route to the town to rescue survivors, the Associated Press reported.

He has advised motorists to avoid nearby roads to facilitate the arrival of rescuers, ambulances and first responders.

“The most important thing right now is to save lives,” Mr Gutierrez said, according to the Associated Press.

Eduardo Rivera, director of a hospital in Guatapé, told Colombian news publication Teleantioquia that three people had been confirmed dead. This has since been updated to nine.

Head of Colombia’s police General Jorge Nieto said 24 people were being treated for injuries at a local hospital.

It is currently unclear what caused the boat to sink but survivors have told local media that they suspected the boat may have been overloaded.

More to come