Export uptick a 'warming' trend

"After mixed conditions in the first quarter, commodity imports picked up momentum in April. Looking ahead, constructive global growth in the coming quarters will likely support gradual improvement in China's export sector," Zhu said.

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Exports to the European Union rose a seasonally adjusted 7.8 percent in April, compared with a rise of 6.9 percent in March. Exports to the US expanded 11.2 percent, compared with a 2.4 percent drop in March.

Exports to Japan fell 1.4 percent, in contrast with a 20 percent gain in March.

Exports to the Association of Southeast Asian Nations grew 1.7 percent in April, down from a 23.3 percent rise in March.

Shipments to Hong Kong fell 4.5 percent in April, compared with a 3.7 percent drop in March, according to Zhu.

Much of the fake invoicing activity took place via Hong Kong.

Despite the modest improvement in April, exporters face an uphill climb. Exports of the world's largest merchandise trader have been losing steam this year. The 115th China Import and Export Fair, also known as the Canton Fair, reported the lowest export volume since 2009 as the fair concluded on Monday in Guangzhou. Export deals dropped by 3 percent from the autumn session to 194.61 billion yuan ($31.7 billion).

The State Council, China's cabinet, announced measures on April 30 to stabilize the "severe and complicated" foreign trade situation, including encouraging imports of advanced equipment, key parts, scarce resources and consumer goods, expanding services trade, cutting the export inspection list and ending some fees.