Renewed my M'sia passport. Do i need to transfer my china visa to new passport or carry 2 passports?

I just renewed my Malaysia passport at High Commission in Singapore. I applied my China Visa on my old passport. Do i need to transfer my China Visa from old passport to new passport or need to carry 2 passports (old and new) to China? If i have to transfer my China Visa to new passport, how to do it, how much it costs and how long it takes or should i do it through travel agency or i have to do myself? If i have to do myself, where should i go to do it? Thanks