A strong aftershock rattled the area near the dangerously swollen "quake lake" in southwest China on Sunday, triggering landslides on nearby mountains, state media reported.

The state-run Xinhua news agency said in a brief dispatch that the aftershock, which took place at 6:51 pm (1051 GMT), had caused "massive landslides", adding that the impact on the "quake lake" was being monitored.

Xinhua said the magnitude of the aftershock was not known.

The US Geological Survey reported a 5.0-magnitude earthquake at the exact same time, with its epicentre located 70 kilometres (45 miles) northwest of quake-hit Mianyang.

The Tangjiashan "quake lake" formed as a result of the devastating May 12 earthquake in Sichuan province, which triggered a huge landslide that blocked the Jianjiang river, creating a massive body of water.

The lake has become one of the most pressing issues in the aftermath of the May 12 quake that struck mountainous Sichuan, killing 69,136 and leaving 17,686 others missing, according to the latest toll issued Sunday.