This is the nerve-wracking moment two children were spotted climbing over a balcony on a high-rise apartment block.

Terrifying footage shows the siblings clinging to the railing on the 13th floor of the building in Guizhou, China.

Moments later, one of the boys grabbed the window panel and hung his feet in the air, attempting a pull-up on August 7.

Wanting to scream, a worried resident who witnessed the toddlers on the verge of falling remained silent, careful not to startle them.

The concerned onlooker said: 'I didn't dare wait even a minute. I immediately contacted the property, and within about two minutes, the security guards and parents rescued them.'

Apartment management confirmed that the children's father was not at home and that they had been left unattended.

They said: 'We quickly reached out to their father, and our security guards rushed to the apartment and brought the children back immediately.'