David Cameron has hailed the Paralympic Games as an event to fill the country with pride as a ceremonial cauldron was lit in London's Trafalgar Square to launch the torch relay.

The Prime Minister watched as Claire Lomas, who became the first person to complete a marathon in a bionic suit, lit the cauldron from the English national flame kindled on Scafell Pike earlier this week.

London mayor Boris Johnson and London 2012 chair Seb Coe were also at the ceremony, which took place on the north terrace of the square outside the National Gallery.

Speaking in Trafalgar Square, Mr Cameron said: "The Olympic Games made our country proud. I believe these Paralympic Games will make our country prouder still. Already this is shaping up to be the best, the biggest, the most incredible Paralympic Games ever.

"Over these next two weeks, we're going to have more of those moments that will bring us together and make us proud. We are going to show the whole world that when it comes to putting on a show, there is no country like Britain and no city like London."

Ms Thomas, who was left paralysed from the chest down following a horse-riding accident in 2007, walked the London Marathon earlier this year in a pioneering robotic suit, raising £204,000 for Spinal Research. After she lit the cauldron, 26 flame ambassadors each collected a splinter of the flame in a lantern to take back to celebrations being held around the country.

The flame is visiting a number of London's most famous landmarks on Friday as the capital gears up for the start of the Games. Before the cauldron lighting, the torch visited the Royal Opera House. It will later be carried in front of performers preparing for the Notting Hill Carnival, visit the Houses of Parliament and be taken on the Docklands Light Railway (DLR) as it travels around the capital.

London Mayor Boris Johnson said London's Paralympic Games would "dazzle the world". He said: "1948 was an amazing year for this country. The NHS, the first Land Rover, the first Routemaster bus was planned, Shakin' Stevens was born somewhere in Wales, and the Paralympic movement, which is something that's grown massively now.

"The success of the Paralympics tells us something about Britain and the way the country has changed. The Olympics showed what we can do and I think the Paralympics will show what kind of people we are, what's going on in our hearts."

Lord Coe later said organisers "would do what they can" to fill any untaken accredited seats during the Paralympic Games but denied there had been empty seats at Olympic venues.