BEIJING, July 25 (Xinhua) -- China's consumer price index (CPI), a main gauge of inflation, is expected to grow 1.8 percent in 2018, according to the country's top economic planner.

Inflation will stay within a range set by the government this year, and trade frictions will have a relatively small impact on China's domestic prices, said Guo Liyan, a researcher with the National Development and Reform Commission (NDRC).

China is aiming to keep annual CPI growth at around 3 percent this year, the same as the target for 2017.

A surge in international oil prices has been the main boost to a 2-percent CPI growth in the first six months, Guo said in an article released by the NDRC's official WeChat account Tuesday.

The growth of the price indicator is expected to narrow in the second half of the year amid steady production and demands as well as weakened carry-over effects, Guo said.

The producer price index (PPI), which measures costs for goods at the factory gate, is forecast to grow 3.5 percent this year, she said. It registered a 3.9-percent year-on-year growth in the first six months.

In the January-June period, the gap between the growth of CPI and PPI narrowed by 3.3 percentage points compared with the same period last year, Guo noted, calling it a reflection of the strengthened effects of supply-side structural reform in key areas.

The general level of China's market prices will remain stable in the second half of the year, leaving room for the fine-tuning of monetary policies and helping sustain steady economic growth, Guo said.

China's GDP expanded 6.8 percent year on year in the first half of 2018, up from the annual target of around 6.5 percent and within the range of 6.7 percent to 6.9 percent for 12 consecutive quarters.