A 24-hour service has been launched for NHS patients, offering GP consultations via videolink on smartphones.
The pilot scheme will initially cover 3.5 million patients in greater London.
Patients will be able to check their symptoms through the mobile app and then have video consultations within two hours of booking.
The Royal College of GPs has warned the service may not help patients with complex needs.
The new free service has been launched by a group of London GPs and the online healthcare provider Babylon.
Patients joining will leave their existing practice, with their records transferred to a group of five central London surgeries.
Dr Mobasher Butt, who is part of the team behind the GP at Hand service, told BBC Radio 4's Today programme: "It's high time that NHS patients were given the opportunity to benefit from technology to improve access to healthcare.
"We've benefited from this kind of technology in so many different aspects of our lives, whether that be shopping or banking, and it's really time that we were able to do that in healthcare for NHS patients."
Jane Barnacle, director of patients and information at NHS England London, said GP practices were right to carefully test innovative new technologies that could improve free NHS services for their patients while also freeing up staff time.
But the Royal College of GPs is concerned the new service might only work for younger healthier commuters and not those with complex health conditions.
Prof Helen Stokes-Lampard, who chairs the RCPG, said: "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.
"We are also concerned that patients are being given the option of switching back to their local surgery if they are not satisfied with the level of service offered by the app.
"As well as issues with patient confidentiality and the safety of the patient record, it is hard to see how this could be achieved without adding to the huge burden of red tape that GPs are already grappling with.
"While this scheme is backed by the NHS and offers a free service to patients, it is undoubtedly luring GPs away from front-line general practice at a time when we are facing a severe workforce crisis and hardworking GPs are struggling to cope with immense workloads."
Dr Richard Vautrey from the British Medical Association said: "This approach risks undermining the quality and continuity of care and further fragmenting the service provided to the public."
GP at Hand strongly deny that care would be compromised in any way.