Items including diamond earrings and a diamond Rolex watch were taken from her £32million Belgravia mansion after a property viewing.
"The theft occurred at the London house during a property viewing," a spokesperson told the Mail Online. "The family were not home at the time. No further comment will be made."
The 24-year-old discovered that the jewels were missing after someone who reportedly posed as a property buyer looked round the house.
Petra, who is the youngest daughter of billionaire Bernie Ecclestone, found them missing from a bedroom nightstand, according to reports.
After the theft, household staff were searched by security but were found to be clean.
The potential buyer, who called himself Oleg, is reported to have viewed a number of other multi-million pound homes in the area.
It is thought that he was left alone in the house by the estate agent.
Petra, whose main home is in Los Angeles, has been spending time in the capital this summer with her husband James Stunt, their baby daughter Lavinia and her sister Tamara Ecclestone.
Lavinia was born at the end of February. Petra gave birth in a London hospital flew back to LA shortly after the birth, where she lives in The Manor, the former home of Aaron and Tori Spelling, which she purchased for a reported $85million in 2011.