Google has been working for some time with several major app players, such as Airbnb TicketMaster and Uber, to bring Android Pay to the in-app checkout.

During its I/O developer conference on Wednesday, the firm promised to make the API available to all developers selling goods and services in markets where Android Pay is available. In addition, a new Android Instant Apps offering promises to give users the ability to pay using Android Pay with a single tap.

In an intriguing new development, the company has also partnered with Bank of America to test cardless ATM withdrawals with just a tap of the phone. The initial rollout to 2,400 ATMs across the country is taking place this month, with palns to extend the service to the bank's 5000-strong national estate by the end of the year. Bank of America is the only bank name-checked at the conference for the cash-on-tap service, but others are bound to follow.

Meanwhile, a new web API, called PaymentRequest, is being developed by Android with the Chrome team to bring Android Pay to mobile web checkouts. The system will be standard across web browsers through the World Wide Web Consortium (W3C).

In addition, the Android Pay API has been boosted to enable users to add offers, loyalty cards and gift cards in the app with the tap of a button. New customers can also be enrolled into loyalty programmes either in store via a NFC tap or through a sign-up page linked from an Android Pay transaction notification.

Pali Bhat, senior director, product management, says: "We believe that mobile payments can make for a better, more secure shopping experience - so we're in this together for the long haul. We’re building a robust Android Pay ecosystem, one that’s open and scalable, to enable developers to drive mobile payments - and their businesses - forward."