The provision of free GP care for under sixes has forced out-of-hours doctors to turn away a "frighteningly large number" of other patients over Christmas.
GP practices around the country continue to be stretched to capacity and are unable to meet demand.
Dr Illona Duffy, medical director of North East Doctor on Call (NEDOC), warned of an "imminent collapse" in general practice if there isn't major reform.
"There is no doubt that the under sixes are having a huge impact on GPs' services," she said.
"During the holiday season we all put out extra staff, expecting a high demand but this just wasn't enough.
"The general practice field was already suffering a crisis, but introducing free medical care for the under sixes was a tipping point.
"The simple fact is that there just isn't enough GPs.
"Doctors around the country had to turn down a frighteningly large number of patients over Christmas.
"Before Christmas, 29 people tried to join our practice and we had to tell them we had no space."
The NEDOC medical director warned the extra pressure on out-of-hours doctors is resulting in more referrals to emergency departments.
"People waiting an unreasonable time to see their GP would instead go to A&E with minor issues like ear and throat infections," she said.
"Other patients with more complex medical problems are also being released from hospital far too early, which means they're coming back into their community just as sick."
Following the introduction of free medical care to under sixes, the Government had suggested children aged 12 and under would soon be able to avail of this service.
However, Dr Duffy said that doctors around the county would fight "tooth and nail" to stop that happening.