China's crude oil processing output in April was 38.32 million metric tons, up 2.5 percent year-on-year, according to the National Bureau of Statistics on Monday.

Analysts said the growth rate was much lower than the same period last year, mainly due to seasonal maintenance at refineries.

"According to our survey, maintenance was taking place in April at most refineries in northeastern China and northern China, which were being prepared for increased demand in the middle of the year," said Jing Ting, an analyst at the oil department of JYD Online, a bulk commodity consultancy in Beijing.

In addition, she said weak market demand also contributed to the slowing crude processing output in April. However, she predicted that demand would gradually grow in the following months.