The darkening outlook was underlined by data showing the fourth monthly decline this year in exports from South Korea, the first major economy to report May numbers, as shipments to the United States, Europe and China all fell.
China's official purchasing managers' index - covering China's biggest, mainly state-backed firms - fell more than expected to 50.4 in May, the weakest reading this year and down from April's 13-month high, with output at its lowest since November 2011.
The separate HSBC China manufacturing PMI, tracking smaller private sector firms, retreated to 48.4 from 49.3 in April - its seventh straight month below the 50-mark that demarcates expansion from contraction - with the employment sub-index falling to 48.1, its lowest level since March 2009.
"What's really worrying is new orders have started to shrink and inventories have started to build up at an unusually fast pace," said Dariusz Kowalczyk, senior economist and strategist at Credit Agricole CIB in Hong Kong.
"Growth in quarter two is likely to slow, probably below 7.5 per cent year-on-year. That puts the annual growth target at risk and the risks continue to increase because the external environment is weakening."