Hong Kong's Hang Seng index tumbled on Monday as HSBC reported showed the manufacturing activity in China kept contracting in April and investors remained cautious before the final round of French presidential elections. Hang Seng index fell 1.84% or 386.25 points and settled at 20,624.39 with only two companies ending in green area. HSBC Holdings declined 1.8% and China Life Insurance sank 2.8%. Aluminum Corp. of China plunged 3.9% and Jiangxi Copper gave up 1.5%.