At least 30 people, including a number of children, drowned after a passenger boat sank off the Comoros islands early Tuesday.

Officials say the death toll could rise, as more than 100 people were on the boat.

It was not immediately clear what caused the sinking. Rescue and recovery operations were continuing in rough seas.

Comoros is a group of three islands off the coast of Mozambique. The vessel was traveling between the main island of Grande Comore and the island of Anjouan.