China's trade surplus rose to an unexpectedly high $22.45 billion in May compared with a $16.9 billion surplus in April.
The increase, likely to intensify calls for Beijing to let the yuan appreciate more rapidly, comes a day ahead of a meeting between
Chinese Commerce Minister Bo Xilai and EU Trade Commissioner Peter Mandelson where trade tensions will be discussed.
Conscious of the need to reduce its economy's reliance on exports, Beijing has introduced a range of measures in recent months - including cutting export tax rebates for some products.
Many of the measures to curb exports took effect at the start of June and that could have played a part in pushing up the surplus in May, as some exporters sought to front-load shipments ahead of the deadline, said one analyst.
Exports grew in May by 28.7 per cent from a year earlier, compared with economists' expectations of a 26.2 per cent rise, the customs administration said. Imports rose 19.1 per cent, below the forecast of 21.0 per cent.
Persistent surpluses have angered Beijing's trading partners, who are increasingly pressing it to take steps to ease the imbalances - notably by letting the yuan appreciate more quickly.
A delegation of senior Chinese officials met in Washington last month with US officials who say the Chinese currency is unfairly undervalued.