Can I get a visa to China mainland from Macau with a UK passport

Hello.

I have a UK passport and will be visiting Macau after 2 days. For this I understand I do not need a visa.

However, I do want to visit mainland china (guangzhou and Shanghai) for 2 or 3 days. Is it possible to get entry permit from Macau? If so, how long does that take? I do not have enough time to apply for a China entry permit in the UK.

Thank you