At least three American mothers and six children from a Mormon family were killed in a shooting in the Mexican border state of Sonora on Monday in an attack blamed on drug cartel gunmen.

Seventeen family members from the LeBaron and Langford families were 'ambushed' eight miles apart while heading to celebrate a wedding anniversary in three cars from La Mora - a decades-old settlement founded as part of an offshoot of The Church of Jesus Christ of Latter-day Saints.

In horrific scenes, gunmen opened fire on one child running away before torching a car as family members burnt to death while trapped inside. Other young children managed to escape and hid by the roadside while a mother was shot in the chest as she put her hands up to surrender. 

A relative said a boy concealed his wounded siblings - some less than a year old - in bushes before he ran back to the nearby town to get help after his mother was gunned down.