NSW's addiction to coal royalties shows no sign of easing, after a surge in coal prices lifted expected royalties for the state by $839 million over four years.

In a budget that offered no hint of how the Berejiklian government would make good on its pledge to cut NSW's emissions to net-zero by 2050, the Treasury forecast royalties – most of which come from coal – will jump to $1.56 billion for the 2016-17 year from $1.19 billion a year earlier.

Limits imposed by the Chinese government on domestic coal in 2016 prompted "substantial coal price rises", which may have "a significant influence on future prices", the government says.

The unanticipated boost amounts to $301 million for the fiscal year about to end, with a further $538 million in extra royalties tipped for the years to 2019-20, compared with last year's predictions.