The Observatory (HKO) on Friday said a 4.2 magnitude earthquake stuck the sea south of Guangdong.

The forecaster said more than 10 people in Hong Kong reported feeling minor shaking sensations for a few seconds.

The HKO said the quake hit the waters south of Shanwei city at 2.40pm, with the epicentre around 200 kilometres south-east of Hong Kong.

The tremor's focal depth was about 10 kilometres.

"Initial estimate gave a local intensity of III (three) on the Modified Mercalli Intensity Scale, that is felt indoors. The vibration was like passing of light trucks," the HKO said.