This is what remains of a Mexican tour bus that skidded off the road Friday leaving 21 dead.

At least 29 were injured in the crash, in the state of Nayarit.

Officials said children were among the dead, but it wasn't known how many lost their lives.

The bus -run by Express Oro Tours - was heading to a resort in Narayit.

Investigators say brake failure and driver fatigue could have played a role in the fatal crash.

Andrew Raven, Reuters