Britain's Prime Minister David Cameron, heading into what is set to be the tightest election in a generation, is expected to lay out plans to extend services available under the National Health Service to seven days a week by 2020.

Cameron, who will speak at his Conservative party's conference in Manchester on Saturday, is expected to say more hospitals must provide top-level care at the weekend, starting with emergency care.

The announcement follows opposition Labour leader Ed Miliband's speech on Friday, when he put the future of the treasured but expensive state-funded health system at the heart of his campaign to oust Cameron.

Health Minister Jeremy Hunt said the NHS plan to extend weekend services would help cut to help cut mortality rates.

"The truth is, mortality rates are higher if you are admitted at weekends, 11 percent higher if you are admitted on a Saturday, 16 percent higher if you are admitted on a Sunday," he told BBC Radio 4's Today Programme.

"Illness doesn't just happen Monday to Friday, it happens 24/7 and that why this next step is a really, really important one," he added.

Labour Shadow Health Secretary Andy Burnham said Cameron needed to set out clearly how the NHS would be funded.

"David Cameron's plans are simply not credible without the extra staff the NHS needs so it has time to care," he said.

"With the NHS in increasing financial distress, David Cameron must set out clearly how it will be paid for. His extreme plans for spending cuts will mean they won't be able to protect the NHS," he added.

Polls put Miliband and Cameron neck and neck ahead of the May 7 vote, the outcome of which could influence whether Britain leaves the European Union or Scotland launches another bid for independence.