Do I need to apply for a Chinese visa, a Chinese travel document or none of the above?

You don't need to provide them. You can enter mainland China by bring your passport and Mainland Travel Permit for HK & Macao Residents. Don't worry.

Thanks Floy. But my travel agent said I need to apply for a visa. I did exactly what you said before, and I was lucky to go through. I was asked for my passport when I exit China using the Mainland Travel Permit. There is a guy encountered the same and the officer told him it was not legal but let him through.

I search google and found out that even if I apply for a visa, I would not get it because I was born in Hong Kong (effective 20160202). However, I could not find this new rule anywhere in the official China Consulate site.