The man had taken his two boys on the trip but is said to have left one behind when he got tired.

A rescue worker said the site had been struck twice as civilians gathered for a meditation retreat.

Four people are still missing after Friday's attack which killed 16 and left 130 injured, including a number of children.

More than 300 companies are showcasing the latest advances in robotics at the five-day event in Beijing, China, organisers say.