China's oil demand growth accelerated to 13.5 percent in May, nearing the explosive rate of 2004, as refiners boosted output and curbed exports ahead of a domestic price increase to meet peak summer demand.

The rebound from last year's tepid 3 percent rise appeared in full swing, but some analysts cautioned that the second half of the year could see a slowdown as Beijing moved to cool down its economy and consumers feel the impact of higher pump prices.

China raised gasoline and diesel prices late last month by a bigger-than-expected 10-11 percent, but the increase still left domestic rates well below international costs, deterring additional imports that could have boosted demand data even more.

The International Energy Agency (IEA), which expects China's demand to grow by 5.7 percent this year, said earlier this month that the pump price rise might help improve short-term demand indicators, but could dampen growth in the longer term.

The surge in May data raised apparent demand growth to 6.5 percent in the year to date, the Reuters calculations showed.