Hundreds of thousands of NHS workers, including nurses, midwives and ambulance staff, are staging four-hour strikes as part of a pay dispute.

Members of 11 unions are walking out from 7am in England and 8am in Northern Ireland in protest at the coalition's decision not to accept a recommended 1% wage rise for all NHS employees.

More than 400,000 workers will join the strike, which will be followed by a work to rule for the rest of the week.

Unison leader Dave Prentis said the strike, the second in a month, should "sound alarm bells ringing" in Westminster because of the anger of such dedicated workers.

Unions have struck pay deals with the devolved administrations in Scotland and Wales, but they are angry with Health Secretary Jeremy Hunt, who they accuse of refusing to engage with them.

Cathy Warwick, chief executive of the Royal College of Midwives, said: "I am very heartened to see that public support for a 1% award for NHS staff has remained high, so we know the public are behind us.

"This is not about our members demanding huge banker-sized bonuses or asking for the similarly large bonuses and pay increases given to many senior managers in the NHS.

"It is about our members having to fight just to get the very modest 1% pay award recommended by the NHS Pay Review Body.

Around 150 police officers in London will help drive or crew ambulances to help the London Ambulance Service with its contingency plans for dealing with the industrial action.

A Department of Health spokesman said: "NHS staff are our greatest asset and we want to make the current pay system fairer.

"We have taken tough decisions to increase the NHS budget but we can't afford a consolidated pay rise in addition to increments without risking 10,000 frontline jobs."