This is the heartwarming moment a sweet schoolgirl helped her big sister sleep comfortably inside a train - propping up her head when it was drifting towards the stranger sitting next to her.

The caring youngster was travelling home with her family when she noticed her dozy sibling kept nodding her head back and forth on her seat in Bangkok, Thailand on February 7.

Touchingly, the little girl pulled her sister towards her so she doesn't fall asleep on the man's shoulder and kept her safe.

Touching footage shows the loving little sister holding her sister's cheek and patting her on the chest to wake her when she almost fell.

Proud relative Arm Eitai said: ‘She has always been protective of her sister. We taught them to be careful and take care of each other when outside the house.

‘I was touched when I saw her do that. I didn't ask her to help her sister. She just did it using her own judgments.'