Apple has introduced a new bigger iPhone for the first time, called the iPhone 6 Plus.

At an event in California, CEO Tim Cook said: "Today we're launching the biggest advancement in the history of iPhone."

The new iPhone 6 Plus comes with a 5.5-inch screen, compared to the four-inch screen of the current generation iPhone 5s.

Apple also introduced the iPhone 6, which is also larger, now coming with a 4.7-inch screen. Both devices also have what Apple call "ion-strengthened glass" screens.

The larger of the two new devices, the 6 Plus, also allows for apps such as Messages and Mail to be displayed in landscape orientation for the first time.

The firm also confirmed a new processor chip, the A8, which will be used to power new apps and games, with partnerships with game studios including Disney and EA also confirmed on stage by Apple's Phil Schiller.

The Cupertino-based technology giant had been expected to announce two new iPhones, with speculation and alleged leaks appearing online over the last few weeks.

The new iPhone devices will ship on September 19, with the company's new mobile operating system, iOS 8, becoming available on iPhone 4s and above from September 17.

Mr Schiller confirmed that the new iPhone 6 will be priced at 199 US dollars (£123) for the 16GB model, going up to 399 US dollars (£248) for the 128GB model. The iPhone 6 Plus will start at 299 US dollars (£185).

Apple has also announced plans to enter the payment market.

"Our vision is to replace the wallet and we're going to start with payments", said Mr Cook.

He also called magnetic strips on credit cards "outdated and vulnerable" before introducing Apple's take on the area.

"We love this kind of problem. This is what Apple does best. We've created a new payment process and it's called Apple Pay," he added.

The new software uses the fingerprint scanner on your phone and native payment apps to allow users to pay for products by touching their iPhone to payment outlets.

It uses near-field communication (NFC) technology, used in existing contactless payments, and the company's own Passbook app to secure your details.

The Find My iPhone app would be used to track and suspend your account if the device is stolen.

"We are not in the business of collecting your data", said Apple, confirming that all Apple Pay transactions are not logged by the company.

Major retailers have already signed up to use Apple Pay in their stores, including Toys R US and Staples.

Online, it is also possible to pay within some apps. For now, the technology is just been introduced in the US.

Apple has entered the smartwatch market for the first time, with the Apple Watch.

"I am so excited and I am so proud to share it with you this morning. It is the next chapter in Apple's story," said Mr Cook.

"Apple Watch is most personal device we've ever created."

The Apple Watch was described as a comprehensive health and fitness interface, and the traditional watch crown, which Apple calls the Digital Crown, is used to control the interface. Mr Cook compared it to the innovation of the mouse on the Mac, and click wheel on the iPod. The crown can be used to scroll through lists as well as zoom in on images and maps.

A huge array of designs and straps were shown on-stage, before the audience rose to give Mr Cook a standing ovation. "It's incredibly customisable", he said. The Apple Watch works directly with iPhone, but has its own native version of iOS.

Rivals Samsung launched their first smartwatch last year, and currently have several on the market. This is Apple's first piece of wearable technology and also follows on from Google introducing their Glass headset, and Android Wear smartwatches.

The Apple Watch has a flexible Retina display, and the screen can sense force used when tapping it. Apple also confirmed that the device will come in two sizes.

There are three collections of the Apple Watch - Apple Watch, Apple Watch Sport and Apple Watch Edition.

The new Apple Watch can be completely customised to suit the style of the user, and also comes with Apple's voice assistant Siri. It will also work with Apple Pay.

The watch can also be used to personally communicate with friends - tapping their name and sending a vibration to the sensor in their own device. Apple also say it is possible to send a replica of your heartbeat to another user. Apple call it Digital Touch, and it also supports drawing pictures and messages on screen in order to communicate.

The device will also be available to app developers through a software development kit, and the Twitter app was demonstrated on stage. Navigation is also on offer through the Maps app.

Apple Watch also comes with health-focused apps called Fitness and Workout, which measure movement and fitness in detail. This will put it in direct competition with Samsung, and the S Health app that Android users turn to for their health and fitness tracking by combining their smartphone and watch.

It can also be used to control Apple TV, as well as serving as a remote control for the camera on a connected iPhone.

Mr Cook confirmed that the Apple Watch will start at 349 US dollars, and will go on sale on early in 2015. "It is worth the wait", he said.