There is no "Pay As You Earn" - it is all assessed in lump sums. So, for example, if you arrive in Septmeber 2004 then you will get a tax return in April 2005 which relates to the tax year 1 April 2004-31 March 2005. You will need to submit this return within 30 days of getting it. You will then receive a tax assessment which will be a bill for the period September 2004 to March 2005 plus a bill for provisional tax for the period April 2005 to March 2006. You will then have to pay this bill in two parts: 75% in January 2006 and 25% in April 2006. At about teh same time you will receive the tax return for the next year, when the bill consists of an adjustment for the previous year (i.e. the difference between the provisional bill and the actual due) plus a further provisional year forward.
As you can see from the timings above, this is actually a better arrangement for the taxpayer than having tax deducted from your pay packet each month. In the example you actually have to pay 13.5 months tax at the end of the first 15 months, and 4.5 months further tax at 18 months. In subsequent years you are effectively paying 9 months tax retrospectively in January and 3 months in April.
The main problem encountered in HK is with people who have come from an environment where tax is deducted each months at source, and are therefore not used to the discipline of putting tax aside. If you come from an environment where you have to put the tax aside each month and then pay it at the end of the year then you won't have any difficulty. Alternatively it is possible to set up an autopay through which you buy tax credits each month if you don't trust yourself to leave the money alone when you put it aside.