| Doctors staged industrial action for the first time in 37 years |
The British Medical Association (BMA) said members will only treat urgent and emergency cases for a 24-hour period while non-urgent care such as outpatient appointments will be postponed.
GP surgeries are expected to remain open although some routine appointments may be rescheduled for a later date.
Accident and emergency departments and maternity services will function normally.
"We are not expecting members of the public to support the action, but we hope they can understand why doctors have been driven to this point -- for the first time in 40 years," said BMA council chairman Hamish Meldrum.
"Patient safety is our absolute priority. We have been clear throughout that any emergency care -- or other care urgently needed by patients -- will be provided.
"We are undertaking this action with extreme reluctance."
The BMA, which has over 100,000 members, announced the action last month but its unclear how many members will actually stop work.
The association says at least four-fifths of NHS secondary care employers have postponed some non-urgent cases.
Doctors are protesting against new plans to raise the retirement age from 65 to 68 by 2015.
Contributions made to the pension pot may also rise.
Health Secretary Andrew Lansley urged doctors not to participate in the "pointless" strike.
"I think if they have an argument and they're angry, they're angry with the government and that's our job to represent the taxpayer and the public interest, and maybe we will have that argument," he told ITV1's Daybreak.
"But I can't see why anybody thinks there is any benefit in penalising patients. It won't serve any purpose whatsoever."