Practices are being opened up to private companies, and to other professions such as pharmacists and nurses.
The walk-in surgeries at Liverpool Street station in London and Piccadilly station in Manchester are open from 7am to 7pm on weekdays - longer hours than those offered by most NHS-run GP surgeries.
Surgeries are also planned for Canary Wharf, Victoria and King's Cross in London, and central stations in Leeds and Newcastle upon Tyne, as part of a £50m improvement of services outside hospitals.
Patricia Hewitt, the Health Secretary, welcomed the development, saying: "The public have told us they want faster more convenient NHS services. Many banks and supermarkets are now open round the clock - the NHS needs to move to match people's expectations for extended opening hours."
Patients can see a doctor or nurse without an appointment and without having to pay. The centres have been operating since the end of last year but were officially launched today.