On Thursday, Hebei-based Great Wall Motors (GWM) and rival BYD entered into a public spat. 

GWM said it had reported to Chinese environmental regulators that two of BYD's best-selling hybrid models, Qin Plus and Song Plus, failed to meet emissions standards.

On its WeChat account, GWM accused BYD of using non-pressurized fuel tanks in these two models, resulting in substandard pollutant emissions. "The company has filed the documents to China's ecology and environment ministry, the industry and information ministry, and the top market regulator on April 11," GWM wrote.

In response, BYD rejected the accusations, arguing that GWM's testing procedures were not valid and that their vehicles complied with national emissions standards.

BYD's official statement indicated that Great Wall appeared to have purchased BYD vehicles and run its own tests without third-party inspection and based on longer test distances required by China's regulations.

"The company is firmly opposed to any form of unfair competition and reserves the right to initiate legal proceedings. The company is open to having the relevant authorities do the review work at any time," BYD wrote.

At the end of the statement, BYD added that, "We hope everyone will act in a way that is beneficial to the industry and Chinese brands. The development of the new energy vehicle business has not been easy."

Following the spat, GWM's Hong Kong-listed shares closed down 7.3%, while BYD's Hong Kong-listed shares fell 5.4%.

BYD, which dominates China's NEV market, nearly doubled sales in April from a year earlier to 210,295 units, while GWM sold 14,863 NEVs, a year-on-year increase of 284.06%.