China's top security chief has urged police across the country to safeguard social stability for the upcoming Communist Party congress that will see China's top leaders be replaced.

The official Xinhua News Agency on Saturday quoted Zhou Yongkang as saying the police had to resolutely safeguard social stability for the congress. It did not say what possible threats there could be.

Communist Party boss Hu Jintao, who is also China's president, will step down at the congress after 10 years in charge and will be replaced by Xi Jinping.

Authorities have still not said when the congress will be held, although it is widely expected to be in the second half of October.