Wikipedia suggests that "Macau" is from Chinese:
Mage (妈阁 "Pavilion of [the goddess] Mazu").
Etymonline seems to suggest it is from the Chinese:
Ma'ao (妈澳 "Bay of [the goddess] Mazu").
Another possibility would be:
Magang (妈港 "Harbor of [the goddess] Mazu").
with the nasal -ng being rendered as a nasal vowel -ao.
Any Portuguese sources on which is correct? Would "-ao" be likely added a Portuguese suffix to a Chinese root?