By Brenda Goh and Roxanne Liu SHANGHAI (Reuters) -Authorities began locking down some western areas of Shanghai two days ahead of schedule, as new COVID-19 cases in China’s most populous city jumped by a third despite stringent measures already in place to try to stop the virus spreading. Home to 26 million people, China’s financial hub is in the third day of a lockdown officials are imposing by dividing the city roughly along the Huangpu River, splitting the historic centre west of the river from the eastern financial and industrial district of Pudong to allow for staggered mass tests. While …