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Nine students have been stabbed to death and 10 injured in a knife attack outside a school in northern China, officials say.

A man suspected of carrying out the attack is alleged to be a former student taking revenge for having been bullied at the school.

The assault took place near Mizhi County Number Three secondary school in Shaanxi province as the students were heading home for the day.

The suspect remains in custody.

Chinese police have given his surname as Zhao and say he is 28.

Their preliminary assessment is that he was motivated to take revenge because he was bullied in his third year (where students are typically aged 13-14).

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Police say the dead are seven girls and two boys.

Photos on social media showed several young students lying on the ground in Yulin city, surrounded by shocked onlookers.

The attack happened at the school at around 18:10 local time (10:10 GMT) on Friday, a local government statement said.