Colombian authorities said nine people died and 28 others have been reported missing after a tourist boat ferrying around 170 passengers sank in the Penol-Guatape reservoir on Sunday, Reuters reported. The cause of the accident has not been declared yet. A rescue operation is underway at the popular tourist destination.

Social media videos of the incident showed several people on several motorboats rushing to the site to rescue passengers still afloat on the upper deck of the vessel. “Ninety-nine people were rescued immediately and 40 more got out on their own,” Margarita Moncada, the head of disaster relief for Antioquia province, told reporters.

Survivors said they heard a loud noise before the boat sank. “Rescue workers and the air force are helping passengers at the scene, President Juan Manuel Santos said on Twitter.