Nextbigfuture calculates that China is already at $13.35 trillion and should end 2018 at $14.5 trillion. This would mean China would have more GDP than Eurozone plus another Spain.
The eurozone consists of Austria, Belgium, Cyprus, Estonia, Finland, France, Germany, Greece, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Portugal, Slovakia, Slovenia, and Spain.
China's GDP was over 82.71 trillion yuan [$12.84 trillion] in 2017. The Exchange rate was 6.45 at the end of 2017.
At the end of March, 2018 China's GDP is about 84.5 trillion yuan which is USD13.35 trillion at the 6.33 exchange rate.
In Match, 2018, China+Hong Kong + Macau GDP is UDS13.75 trillion.