If you open a local multi currency bank account you should be able to transfer foreign currency over to it in much larger amounts.

You will probably have to transfer the cash from Singapore in USD if you cannot find a bank that has SGD as a currency you can hold.

Once the funds are on deposit you can go into the brach with your passport and ask them to convert it to RMB. They will ask what the money is for, but it's more so they can fill in a form these days than anything else. Merchants bank used to have a limit of US$5000 being converted each day, but that seems to have gone now as last time they let me do more without comment.

You will pay a small transfer charge, but this is usually compensated by the fact that the banks give you a better rate than if you were exchanging notes and there are then no charges from a foreign ATM.

why not cash out in Singapore in larger currency notes and carry on you into China, thought there is a limit of how much u can bring in but big notes is easy to bring in.

Then get a local who u know well and go to bank together to change them into RMB (think there is no limit for local to change from S$ to RMB)