The geopolitics of the art world are shifting.

On Wednesday, the 21st edition of the Frieze London fair in Regent’s Park opened for V.I.P. visitors, a week before the inaugural Art Basel Paris fair opens in the newly restored Grand Palais. For years, London’s “Frieze Week,” with its high quality fairs, auctions, dealer and museum exhibitions, has been international art lovers’ must-attend event in October. But after Britain left the European Union, a resurgent Paris is presenting serious competition.

The footfall on the preview day of Frieze London, a contemporary art fair, was noticeably less hectic than it has been in previous years. “Frieze is a solid art fair, but Art Basel Paris clearly has the edge,” said Wendy Cromwell, a New York-based art adviser who is attending both fairs this month.

Matthew Marks, David Kordansky, Casey Kaplan and Marianne Boesky, U.S.-based dealers who had been regular exhibitors at Frieze London, were notable absentees at this year’s edition, choosing instead to exhibit in Paris.

Frieze London’s remaining 169 international exhibitors, and those staffing a further 131 booths at the nearby Frieze Masters, the fair devoted to pre-21st century artworks, are hoping the week — both fairs run until Sunday — will re-energize what has been a moribund art market for over a year.

A combination of high interest rates, the economic slowdown in China, political uncertainty in the United States and relentless conflicts in the Middle East and Ukraine have battered the confidence of both buyers and sellers of fine art around the world. Demand at last month’s Frieze Seoul fair was “moderate,” according to The Art Newspaper.