Some mainland residents at an unknown location run for cover.
The Hong Kong Observatory said the earthquake struck at 10.57pm near the coast of southeastern China.
The epicentre was located about 110km west-southwest of Shantou, or about 180km east-northeast of Hong Kong.
The depth of the focus was 16km, according to the mainland's Earthquake Networks Centre.
As of 1am today, no casualties were reported by mainland media.
The Hong Kong Observatory said they received more than 40 reports from several locations including Eastern district, Sha Tin and Sham Shui Po. Some 20 calls were made from western Kowloon.
The quake cause a buzz online with some saying they felt the shaking, while others did not feel the tremor.
"It's really been shaking for some 10 seconds, my home is obviously shaking," an internet user said on the Golden Forum. Another user said: "I felt it a bit earlier."
A mainland netizen said on a microblog: "The shaking felt quite strong. It scared my baby."
Another said: "The bed was shaken once. I felt it right away and immediately brought my daughter to run downstairs."
A Shenzhen resident reported feeling a slight swaying.
They must be having a party! Right, that's it. They've got the music cranked all the way up to 11! Tev that is!