Adventurer Sarah Outen set off on her epic global voyage yesterday, declaring: "Bring on the world!"

The intrepid 25-year-old, from Rutland, began her 20,000-mile journey yesterday by paddling her kayak under London's Tower Bridge.

From there she will cross two oceans and three continents by kayak, rowing boat and bike in a journey which will take two-and-a-half years.

Just before setting off, Sarah said: "I'm feeling so good. I'm a bundle of tears and smiles but I just cannot wait to get into it."

Sarah's mum Helen, brothers Matt and Mike, friends, sponsors and hundreds of other well-wishers including schoolchildren from Rutland, saw her off.

Sarah will cross the English Channel in her kayak, Nelson, before cycling across France, Belgium, Germany, the Czech Republic, Poland, Ukraine, Russia, Kazakhstan, China and then back into Russia.

She will then paddle and cycle her way into Japan, from where she will row solo across 5,000 miles of the north Pacific and then cycle from Vancouver to New York before rowing solo across the North Atlantic.

She would be the first person ever to complete the route and expects to take about two-and-a-half years.

Sarah, from Ashwell, near Oakham, said: "It's really touching so many people have come down to see me off because for lots of the other parts of the journey everybody I meet will be a stranger."

Sarah became the first woman to row solo across the Indian Ocean, in 2009, and raised more than £20,000 for Arthritis Care in memory of her late father, Derek.

Sarah said the most daunting part of her new adventure, dubbed London2London: Via the World would be rowing across the Pacific ocean.

Nearly 40 excited children chosen from 10 primary schools in Rutland travelled to London along with students from Stamford School, where Sarah was a pupil.

Ten-year-old Lucy Hinch, a pupil at St Nicholas School, Cottesmore, said: "I think Sarah is so brave and she must be really scared and worried at the moment."

At 1.10pm yesterday, mum Helen sounded the klaxon which marked the start of her daughter's journey.

Sarah will keep in touch with home via a satellite phone, her blog and through e-mails and letters.

The voyage will raise money for breast cancer awareness charity Coppafeel, The Jubilee Sailing Trust, the Motor Neurone Disease Association and WaterAid.