score:3
I have not seen this case online before, but I'm pretty sure this will happen:
Note that if you realise your card is close to HK$0, you would top it up first to ensure you don't go below HK$35 and have to waste precious time to re-top up before entering the MTR.
Upvote:6
For the tl;dr answer, @B.Liu's comment is correct, if you manage to surpass the maximum negative value on an Octopus card in Hong Kong, you will be required to go to the customer service window to top up your card before you can exit the turnstiles.
Based on personal experience living in Hong Kong, for those who prefer more detail, Hong Kong's Octopus card is more "generous" than many stored value cards. As long as your card has a positive balance at the beginning of a journey, you can enter the turnstiles and leave with a negative balance because the deposit itself acts as a buffer:
[The HK$200 Octopus card] comes with [HK$150 in transit credit and] a refundable HK$50 deposit which covers the card cost and ensures uninterrupted Octopus service in case of negative value (i.e. the convenience limit) of (a) up to HK$35 on a single occasion for On-Loan Octopus issued before 1 October 2017, or (b) up to HK$50 on a single occasion for On-Loan Octopus issued on or after 1 October 2017.
Just as a point of contrast, Singapore's EZ-Link card is different. The initial purchase costs S$10 with S$5 of travel credit and you have to have a positive travel credit balance of at least S$3 to be able to enter the turnstiles at all. The deposit does not act as a buffer:
You will need at least $3 in your stored value travel card before you can start your journey on the MRT/LRT. This ensures that you have enough in your card to pay the required fare when exiting the faregates, even for the longest journey.
In practice, you have to work pretty hard to surpass the Octopus negative balance limit in Hong Kong. I distinctly remember managing to do it once by starting with a negligible balance on a trip between Quarry Bay and Lo Wu en route to Shenzhen (when such trips were easy!). The exit turnstile made a disapproving tone and I had to top up at the window before I could head out of Hong Kong. With a quick review of the Octopus fare chart, long journeys to the border are the ones that you might be able to exceed the limit.
I never have tried this, and it requires a separate tap to enter the first-class train car, but if you just wanted to see how low you can go, you could travel First Class on the East Rail Line — say from Admiralty to Lo Wu — and theoretically obliterate the limit and require a hefty top up at the border. A balance of negative HK$99 or so with this route has to be about as low as you could push it.