Reports soon followed, suggesting the helicopter was in fact called to the palace for an unrelated accident, but hundreds of Twitter users think otherwise.
According to sources, the parking area in St Mary's hospital in Paddington has been cordoned off, and social media is awash with talk of the future Prince/ Princess being on its way.
A Clarence House spokeswoman told a UK newpaper that they would not comment on the current speculation, but that a a formal statement would be provided when the Duchess is admitted to hospital.
The Duchess of Cambridge is due to have Prince William’s first child on Saturday, but it looks like it could be much sooner.
The 31-year-old was due to spend time at her parent's home in Berkshire in the run up to the birth, but insiders say she has instead been based in London in order to be closer to St Mary’s the hospital, where William was also born.
William and Kate married on the 29 April 2011 and on the 14 January 2013 St James's Palace announced that the Duchess was expecting her first child, due in July 2013.