BEIJING, Feb. 7 (Xinhua) -- China's railway project builders have been told to reappraise and renew their environmental approvals to account for major design modifications designed to speed up the trains.

The major modifications include increasing the maximum speed of trains by 50 km per hour, according to a circular issued by the Ministry of Environmental Protection.

Railway design and construction units should compare design changes with their previously-obtained environmental approvals before starting construction, said the circular published on the ministry's website.

Construction units should apply for new environmental assessments and approvals if the new designs substantially alter the scope or content of the projects or include new pollution prevention and environmental protection measures.

According to the circular, items subject to reappraisal also include alterations to train power systems, as well as changes that could possibly harm natural resources or cultural heritage sites.