The Mayor of London continues his six-day trade mission in China today in a drive to encourage closer business links with the UK capital.
It's Boris Johnson's first visit to the country since the Beijing Olympics in 2008.
China is now the world’s second largest economy, worth an estimated $8.2 trillion.
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Paramedics were on standby outside the police cordon as armed officers stood by the property.
A team of researchers has taken samples from the ten busiest London Underground lines to work out which are the dirtiest.
The action comes on top of an emergency timetable which has seen hundreds of trains a day being axed.