BEIJING, Sept 5 - China said it will moderately raise natural gas prices when conditions are right, as part of measures to price resource products at levels that will promote energy-efficiency.

China has been struggling with frequent shortfalls of energy including gas, power and oil in recent years, because low state-set prices have reduced producers' incentives and a booming economy has caused consumption to soar while energy-efficiency has lagged.

"China will align resource product pricing in due time and choose an appropriate opportunity to further align refined oil products prices and moderately raise gas prices...," the National Development and Reform Commission (NDRC) said on Friday.

The NDRC is China's top economic planning agency.

It did not explain under what circumstances it would consider a price change or what percentage might be appropriate.

China raised refined oil prices by nearly 20 percent in July and hiked on-grid power rates twice in the past two months to stem spreading supply woes, but it has kept gas prices unchanged despite domestic demand far outpacing supply.

China's gas prices are half those in the United States and less than one-third those of spot liquefied natural gas imports.

Analysts have said Beijing may raise gas prices as soon as this month to bolster long-term supply while damping short-term demand, although the possible move is unlikely to resonate as loudly as recent power and fuel increases because gas accounts for just 3 percent of China's energy use.