A skyscraper of more than 70 storeys has been evacuated after it started to shake, sending shoppers scrambling for safety in the southern Chinese city of Shenzhen.Local authorities do not yet know what caused the 300m (980ft) SEG Plaza building to wobble on Tuesday afternoon.No earthquakes were recorded at the time. An investigation is under way.The 20-year-old building houses an electronics market and offices.It stands in the heart of Shenzhen, a sprawling city of more than 12 million people known for its shopping and booming tech industry.Footage shared on social media showed hundreds of people running away from the skyscraper...