China's Belt and Road Initiative is the world's largest infrastructure development project aimed at linking Europe and East Africa with Asia. Port infrastructure development associated with the maritime component of China's Belt and Road Initiative (mBRI) could have trans-boundary environmental impacts. These impacts are likely to affect key coastal marine habitats (coral reefs, mangroves, seagrasses and saltmarshes) and threatened marine species. We used spatial analyses to quantify the potential impacts of ports and subsequent increased shipping traffic associated with the mBRI for key habitats and species. Significant areas of individual countries coastal marine habitats could be affected by port development. Over 400 threatened marine species, including mammals, could be affected by port infrastructure, while over 200 threatened species are at risk from an increase in shipping traffic and noise pollution. A project of this magnitude provides an opportunity for a central governing body to develop and implement an overarching environmental framework and policy that mitigates risks to biodiversity.