The goal of finding a treatment to cure or halt dementia by 2025 is "within our grasp", Prime Minister David Cameron has said, as he announced a doubling in UK funding for research into the disease.

Mr Cameron was addressing scientists, politicians and campaigners from around the world who have gathered in London for a dementia summit called by the UK as part of its year-long chairmanship of the G8.

With the World Health Organisation forecasting that numbers of dementia sufferers will almost double worldwide every two decades, Mr Cameron has said he wants UK Government investment in dementia research to double from £66 million in 2015 to £122 million in 2025 - with similar increases from the commercial and charitable sectors.

The London conference is expected to agree to a package of measures on international information-sharing and collaboration in research.

Mr Cameron said he hoped it would mark the point when "the global fightback really started, not just in finding a cure for dementia, but also in preventing it, delaying it and, crucially, helping those with dementia to live well and with dignity."

The PM said he wanted the UK's life sciences industries to play "a leading role" in the fight against dementia.

And he announced three new investments in life sciences, including £200 million from GlaxoSmithKline, £150 million from the Medical Research Council for clinical infrastructure for dementia and genomics and £3 million from Belgian pharmaceutical company UCB for its research centre in Slough.

Mr Cameron told the conference the world should be "just as resolute" in tackling dementia as it had been in the past in seeking treatments and cures for killer diseases like malaria, cancer and HIV/Aids.

"The challenge is huge and we are a long way from a cure, but there is hope," he said.

"We meet with the conviction that human ingenuity can overcome the most daunting of challenges and we meet with the determination that we will take the fight to dementia and improve and save millions of lives."

And he added: "The aim of trying to find a cure or disease-halting therapy by 2025 by a big collective boost to research funding is within our grasp."

Health Secretary, Jeremy Hunt, told a press conference it had been an "exciting day".

"One of the reasons I have come to the issue of dementia is because I think it's one of the last bastions of stigma in illness," he said. "What we do about dementia is really the litmus test for our generation of politicians."

Mr Hunt said the G8 had agreed to work together to find a cure or disease-modifying therapy "to stop dementia in its tracks" by 2050.

A dementia envoy is also being set up to look into attracting other sources of funding for dementia research, including from private companies.

In the NHS, the aim is to ensure that diagnosis rates rise from below half to more than two-thirds.

He likened dementia to how cancer used to be, saying funding for cancer research only stated pouring in once "we stopped sweeping it under the carpet".

Mr Hunt said: "The amount going into research is too little.

"We would like a cure to be available by 2025. It's a big, big ambition to have. If we don't aim for the stars we won't land on the moon."

In a statement, the G8 called on the World Health Organisation to identify dementia as "an increasing threat to global health" and to help countries adapt to the dementia timebomb.

It added: "We recognise the need to strengthen efforts to stimulate and harness innovation and to catalyse investment at the global level."

Jeremy Hughes, chief executive of the Alzheimer's Society, said: "Today the UK has demonstrated global leadership on tackling dementia.

"We have committed to a global plan, better support for people with dementia through research and the Prime Minister has agreed to narrow the funding gap between dementia and cancer research - something we have long campaigned for.

"Charities will play an important role in making this happen and today Alzheimer's Society has pledged a minimum of £100 million over the next decade to dementia research.

"Dementia has come out of the shadows and is centre stage - but we must ensure G8 has a lasting legacy."