The train will make the 7,500 mile, three-week-long journey bound for Yiwu in the Zhe Jiang province in eastern China.
This inaugural export train bound for China departed just under three months after the first ever import train from China arrived in the UK.
The service is part of China's One Belt, One Road programme - reviving the ancient Silk Road trading routes to the West.
After passing through the channel tunnel into France and Belgium, the DB Cargo locomotive will call in Duisburg, Germany before InterRail pull the cargo through Poland, Belarus, Russia and Kazakhstan before the train crosses to Yiwu, China.
Container operator OneTwoThree Logistics is overseeing the transportation and booking of cargo for the UK/China rail freight trains, in conjunction with Yiwu Timex Industrial Investment Co., which is running the service with China Railway Container.
While unlikely to challenge ocean shipping or air freight, the new route will offer an alternative to shippers looking for a speedy or cost effective method of delivery.
Greg Hands, Minister of State in the Department for International Trade, said: “This new rail link with China is another boost for Global Britain, following the ancient Silk Road trade route to carry British products around the world.
“It shows the huge global demand for quality UK goods and is a great step for DP World’s £1.5bn London Gateway Port as it also welcomes its first regular container ships from Asia.”
Xubin Feng, chairman, Yiwu Timex Industrial Investment Co., said: “We are proud to be able to offer the first ever UK to China export train.
“Restoring the ancient Silk Road as a means by which China, North Europe and now the UK can exchange goods is an important and exciting initiative.”