Safety authorities will be watching Hunter Valley coal mines closely, after a spike in cases of dump trucks coming into contact with overhead powerlines.

State mine officials say the elevated trays on dump trucks occasionally come into contact with overhead powerlines or structures, but the increasing rate of such incidents has prompted them to issue a statewide safety bulletin.

Investigators in recent cases say luckily, it has not led to many serious injuries or fatalities, but the potential certainly exists.

They have urged all mines to look over proper work procedures again, and make sure they are followed.

The authorities recommend tray warning devices should be fitted in such a way that they can not be disabled.

They say human error and complacency are big factors too.

Mine safety investigators warn that it is crucial for adequate supervision and training to be provided, and that exclusion zones should be established if powerlines are struck.

This keeps the risk down by keeping people away from the potential explosion of the truck's tyres.

For mine managers, it is a business issue too.

The authorities say several mine sites have sustained substantial damage to powerlines and site infrastructure, significantly affects mining and processing activities.