It was a mere shake - like a truck passing your door - but it was enough to send more than 400 Hongkongers scrambling for their phones to report an earthquake to the Hong Kong Observatory. The 5.4 magnitude tremor struck near Wuzhou in Guangxi with the epicenter about 340 kilometers northwest of Hong Kong. "The observatory received over 400 locally felt reports of this earth tremor. Initial estimates gave a local intensity of III on the Modified Mercalli Intensity Scale - that is, felt indoors - a vibration like the passing of light trucks," the observatory said on its website. Netizens on various discussion forums and Facebook said they felt the shocks in Kowloon City, Wong Tai Sin, Tuen Mun, Fan Ling and Yuen Long. "I thought I was fainting," one said. Another commented: "I felt like my chair was shaking." Netizens in Shenzhen and Guangzhou also said they felt the tremor, with one writing on Weibo that "it lasted for a few seconds." The mainland authority said the earthquake struck at a depth of 10 kilometers but by late last night there had been no reports of casualties in the 360,000-population county.