Chancellor Angela Merkel representing Germany, which currently holds the rotating EU presidency, is to negotiate with Chinese President Xi Jinping as part of high-level talks concerning an investment deal between Beijing and the European Union.
Billions of euros worth of critically endangered eels are trafficked each year from Europe, ending up in China and Japan in what is "the largest wildlife crime on Earth," campaigners say.
As doubts grow over China's 'Belt and Road' trade infrastructure project, the EU is launching an alternative plan for Asia it says will not saddle countries with debt they cannot repay.
Johnson's visit came two months after the European Union announced its decision to resume ties with Thailand following a period of suspended relations in response to a 2014 coup.
Myanmar and Bangladesh this week are likely to discuss repatriating more than 600,000 minority Rohingya Muslim refugees who fled to Bangladesh.