The accident took place at 05:30 local time (10:30 GMT) on the Huallaga River, in Muyuna on Sunday, when a boat full of passengers crashed into a freight barge amid dense mist at dawn, according to state channel TV Peru.
“So far there is an undetermined number of missing persons, as well as 11 dead and six injured,” the National Institute of Civil Defense said in a statement.
Firefighters, policemen and sailors are in charge of the search for those who disappeared.
Local television footage showed survivors crying on the riverbank as authorities carried some bodies away.
The passengers belonged to a religious community that was returning to the city of Yurimaguas after participating in a vigil in a secluded hamlet in the jungle known as Santa Maria.