I spent 6 days in Australia, and applied the Sun block in the trip (30+ is quite the max I can find in any phamacy shop), but I still get serious sun-tanned.

Better to prepare 60+ or even 100+ in HK before going there.

well..................you need to have at least 60+ ..................that's usual common senes in australia..........especially for whole day out-door events

Where did you go? Snorkelling?

DOES IT ENOUGH if i wear long shirts with long sleeves and long trousers?

I went to Tasmania for brush walking.

It is not that common to buy any sun block more than 30+ locally. So better to buy stronger sun block in HK.

oh still get serious sun-tanned in there? I thought that you  were playing Snorkelling...etc...

I'm going to Australia in early March, hopefully it will not that hot and sunny~