Doctors have urged the NHS to delay the national roll-out of a non-emergency phone line, saying "patients' lives will be at risk."
From Monday, the 111 line will replace NHS Direct and GP out-of-hours numbers across most of England.
But pilot schemes have shown disastrous results, with tales of patients waiting hours for advice, and others asked to call back later.
A parent of a sick baby was told by a 111 worker: "I don’t know what to do."
In Wiltshire, where the line was introduced earlier this month, call handlers have been sending ambulances to people with hiccups, sore throats and earache. There are concerns that calls are being handled by staff with just ten days training who read out a series of set questions from their computer.
And yesterday Dr Laurence Buckman, Chair of the British Medical Association’s GP Committee, said: “We cannot sacrifice patient safety in order to meet a political deadline for the launch of a service that doesn’t work properly.
“There have been widespread reports of patients being unable to get through to an operator or waiting hours before getting a call back with the health information they have requested.
“In some areas, such as Greater Manchester, NHS 111 effectively crashed because it was unable to cope with the number of calls it was receiving.
“The chaotic mess now afflicting NHS 111 is not only placing strain on other already over stretched parts of the NHS, such as the ambulance service, but is potentially placing patients at risk. If someone calls NHS 111 they need immediate, sound advice and should not be faced with any form of delay.
“The BMA has been warning the government about the problems with NHS 111 for almost two years. They must act soon to ensure that patient safety is protected.”
Dr John Hughes, a GP in Crumpsall, near Manchester, told the Daily Mail: "I am extremely worried. Within less than 11 hours the service was in meltdown. Calls weren’t being answered for hours, patients were having to ring up 999 ambulances.
"These are non-clinically trained people. They work their way through a computer system which directs them to the next question to ask.
"It really can’t go live on Monday because patients’ lives will be at risk. I have had reports of a 90-year-old lady having to wait more than an hour and a half for an urgent call."
NHS Direct was launched in 1998, providing 24-hour medical advice, aimed at reducing the number of patients needlessly going to A&E.
It was judged a success, but was occasionally overstretched during flu and norovirus outbreaks.
Now it has been merged with out-of-hours numbers for GPs, and callers will be put through to a call centre worker who will decide if they need to go to A&E, a GP clinic, a chemist or can get by with over-the-phone advice.
In some areas the 111 service will be run by private firms while in others it will be overseen by NHS ambulance services.
A spokesman for NHS England, the new body in charge of the health service, said: "The service has great potential to be a fast, efficient, all-round service that ensures patients get the right care for their needs.
"This is a very important service for the public and we will make sure everything is in place to make a safe, high quality service that patients and the public can trust."