The killing of a Japanese schoolboy in the Chinese city of Shenzhen has sparked worry among Japanese expats living in China, with top firms warning their workers to be vigilant.

Toshiba and Toyota have told their staff to take precautions against any possible violence, while Panasonic is offering its employees free flights home.

Japanese authorities have repeated their condemnation of the killing while urging the Chinese government to ensure the safety of their citizens.

The stabbing of the 10-year-old boy on Wednesday was the third high-profile attack on foreigners in China in recent months.