Nine people including three children drowned on Sunday and six people were missing after swimming in a river during a religious camping weekend in western Mexico, Mexican rescue authorities said.

The members of a Christian church group were swimming in a popular bathing spot along the Cuixtla river in Mexico's Jalisco state and were dragged under by the current, a spokesman for Mexico's Civil Protection unit in Jalisco said.

The cause of the accident was not clear.

"This is unusual because it wasn't raining, it is not a particularly big river and many people go swimming at that spot," the spokesman said.