Only life-threatening situations such as cardiac arrest are being immediately responded to as ambulance crews launch strike action today.

Serious conditions which are judged not be immediately life-threatening may not be immediately attended to by emergency teams.

NHS medical director Professor Sir Stephen Powis said: “There is no doubt that the NHS is facing extreme pressure and industrial action will add to the already record demand we are seeing on urgent and emergency care, and so it is really important that the public play their part by using services wisely.

“This means continuing to call 999 for life-threatening emergencies – if it is not life-threatening you may have to wait longer than usual for an ambulance.”

The ambulance strikes involve paramedics as well as control room staff and support workers.

A further ambulance strike is planned for 28 December.

The government has put the armed forces on standby to help out during the action.

The action over pay follows the latest walk out by nurses yesterday.