Does Apple pay work when phone is off (I.e. Battery is flat)?

The contact less payment system is technically a passive system, so in principle Apple pay would work, even if the phone is switched off.

I noticed the Apple watch needs to be synced to an iphone in order for appLe pay to work, which makes me think that Apple pay only works when the phone is switched on?

Problem being that if I use the phone to pay for public transport but the battery is flat by the time I need to go home - how do I pay?