Millions of NHS patients who live or work in various locations in London can sign up to the service, which offers a GP consultation via a smartphone 24 hours a day.
But the Royal College of GPs said that while the scheme may be seen as a golden ticket for some patients, others are not eligible for the service.
The GP at Hand service - created with healthcare technology firm Babylon Health - offers a booking system through a smartphone app, with the promise of a video consultation within two hours of booking.
If a patient needs a face-to-face appointment, they must travel to clinics in commuter hubs.
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Commenting on the launch of the project, Professor Helen Stokes-Lampard, chairwoman of the Royal College of GPs, said: "Technology can achieve wonderful things when used properly, but we are really worried that schemes like this are creating a twin-track approach to NHS general practice and that patients are being 'cherry-picked', which could actually increase the pressures on traditional GPs based in the community.
"We understand that with increasingly-long waiting times to see a GP, an online service is convenient and appealing, but older patients and those living with more complex needs want continuity of care and the security of their local practice where their GPs know them.
"We notice there is an extensive list of patient conditions such as frailty, pregnancy and mental health conditions that are the essence of general practice, and which GPs deal with every day, but which are not eligible for this service.
"While this scheme is backed by the NHS and offers a free service to patients, it is undoubtedly luring GPs away from frontline general practice at a time when we are facing a severe workforce crisis and hardworking GPs are struggling to cope with immense workloads."
Dr Mobasher Butt, GP at Hand partner, said: "We do everything from grocery shopping to our banking online yet when it comes to our health, it can still take weeks to see a doctor and often means taking time off work for an appointment.
"With the NHS making use of this technology, we can put patients in front of a GP within minutes on their phone, so the days of ringing frantically at 8am for an appointment should be long gone.
"This new NHS service makes it easier for patients to see a doctor quickly at any time and from anywhere and doesn't cost the NHS a penny more. It's a win win."
Dr Richard Vautrey, chairman of the British Medical Association's GP committee, said: "While these proposals appear to be focused on making access to a GP easier, in reality it will divert patients away from their GP and practice and leaves them receiving care from doctors who don't know them as well as their own GP would do.
"This approach risks undermining the quality and continuity of care and further fragmenting the service provided to the public.
"It is also delivered by a private company that is primarily cherry-picking younger, generally healthier people and excluding many others.
"It will do nothing to help the growing number of older, vulnerable patients who need well-funded services that can provide the specialist care they need in the community."
Dr Matt Noble, partner at the GP at Hand practice, said: "Claims it will only cherry-pick healthy patients are simply untrue.
"This service is open to anyone within the eligibility area and from our pilots of the service in Essex and West London, we have seen a broad range of patients benefiting from being able to see a GP quickly and at the patients' convenience, including elderly patients who find it difficult to get to surgeries."