* Exports fall in May mostly due to calendar effects

* Shipments to China post sharpest fall since Aug 2009

* Robust exports to EU, U.S. evidence of uneven global recovery

* Trade seen improving, but China slowdown a risk (Adds breakdown figures, analyst and official comments)

By Christine Kim

SEOUL, June 1 (Reuters) - South Korean exports last month suffered their worst decline in eight months as a drop in Chinese demand and the effect from fewer working days more than offset growing purchases by European and U.S. customers.

South Korea, the fourth-largest economy in Asia, said on Sunday exports last month fell 0.9 percent from a year earlier to $47.88 billion, while imports rose 0.3 percent to $42.53 billion. It resulted in a trade surplus of $5.35 billion.

Exports to China plunged 9 percent in May from a year before, setting the fastest drop in nearly five years and eclipsing a stellar 32 percent jump in sales to the European Union and a 4.5 percent rise in shipments to the United States.

Analysts and the government called for caution over the May export data, pointing to distortions arising from unusually long holidays falling in May in South Korea and China.

"In May, China had many holidays along with ours and so that, on top of China's slowdown, steepened the fall in exports. I think it's too early to say that we will continue to see a decline in shipments to China," said Park Sang-hyun, chief economist at HI Investment & Securities.

Partly supporting the view on holiday effects, a Chinese government survey showed on Sunday the country's official Purchasing Managers' Index rose to 50.8 in May from 50.4 in April, indicating its manufacturing activity picked up.

CHINA REMAINS DRAG

In South Korea, there were 1.5 fewer working days in May than a year earlier and this meant the average exports per working day in fact rose 6 percent to $2.23 billion, the second-best on record, from $2.10 billion a year before.

The median forecast from a Reuters survey of 16 economists was for South Korean exports to grow 1.2 percent in May from a year before, but five of them had predicted losses. Imports were seen up a median 4.2 percent.

It was the first decline in exports since January this year and the sharpest since September last year.

As the world's seventh-largest exporter, South Korea is the first major industrial powerhouse to report foreign trade data each month, making its data an important guide on the latest state of the global economy.

The country has some of the world's top providers of smartphones, cars, ships and industrial equipment such as Samsung Electronics Co Ltd, Hyundai Motor Co and Hyundai Heavy Industries Co Ltd.