Environment Minister Robyn Parker and the state's environmental watchdog have been accused of misleading Parliament and the public in a ''systematic cover-up'' of information about whether uncovered coal trains are polluting the air in Newcastle and the Hunter Valley.

The Hunter Community Environment Centre has obtained thousands of pages of documents it says show Ms Parker and the Environment Protection Authority gave public assurances that no elevated levels of coal dust were detected from the trains even after findings from government experts that there was a strong relationship between the coal trains and a spike in air dust particles.

Accused of a "systematic cover-up": Robyn Parker. Credit:Max Mason-Hubers

It says the documents show the methodology used in reports by the coal train operator, Australian Rail Track Corporation, to monitor pollution was flawed.

HCEC spokesman James Whelan says the documents show the EPA prepared a draft press statement saying coal trains did not increase pollution before the agency received the monitoring results.