Ryanair has agreed to buy five more Boeing 737-800 aircraft, taking its order book to 180 new Boeing planes worth over $16 billion.

Ryanair, Europe's largest airline by passenger numbers, said four of the five planes would be delivered in the summer of next year, with the fifth coming in February 2016.

"Now that we have four more aircraft (21 in total) for summer 2015, Ryanair will offer more new routes and increased frequencies to more customers than ever before," the company said.