Mobile payment service provider Square has launched in the UK, marking its biggest global expansion in a push to boost growth while the U.S. market nears saturation.

The U.K. marks the fifth country where Square is available, joining existing markets Canada, Japan, Australia and the U.S.

The U.K. has "always been an example of entrepreneurship and small businesses, not just in London but all over country," Chief Executive Officer Jack Dorsey said in a statement. "That's the same pattern we saw in the U.S. We also now have hardware that's global so it allows us to move much faster" into foreign markets.

Square helps independent traders take card payments and offers competitive rates, no monthly contracts or hidden fees, and next-day settlement on most transactions. It takes minutes to get set up, and sellers can quickly begin accepting payments from Visa, Mastercard and American Express cards. Square's card reader pairs with the free Square Point of Sale software, which includes tools such as real-time sales data, invoicing and digital receipts, all in a single app.

While Square made its start selling square credit card-readers that plug into iPhones or iPads, allowing food truck vendors and other small merchants to process transactions out in the field, it now faces similar offerings from the likes of PayPal Holdings Inc. In the U.K., Square will compete with incumbent players, such as Ingenico Group SA and iZettle.