Satellite images of the Sohae station seen by US-based monitoring group 38 North suggest Pyongyang is complying with a promise made to the US in June.
US President Donald Trump said North Korea's leader Kim Jong-un had vowed to destroy an engine test site, but did not specify which one.
Pyongyang has maintained that Sohae is a satellite launch site.
But US officials suspect that it has been used to test ballistic missiles.
During a landmark meeting between President Donald Trump and Kim Jong-un in Singapore last month, the two leaders signed a deal to work towards the "complete denuclearisation of the Korean Peninsula".