This may sound silly, but I have noticed on the Australian government website that if you already have a valid visa, getting an Australian evisitor visa will make your current visa invalid. Is this correct? I want to apply for one, but I'm afraid it will invalidate my Chinese visa. Im currently in China on an F-visa.
they refer to Australian visas, not to visas of other countries, your Chinese visa will not be invalidated.
One country can not invalidate a visa for another country.
The section you're referencing almost certainly refers to the fact that any another Australian visas will be canceled when you apply for an Australian eVisitor visa - not a visa from another country.