October registrations were slightly worse than Bloomberg Intelligence's projection for a decline of about 6 percent. Sales probably will fall about 5 percent this quarter and finish the year down at least 25 percent, Bloomberg Intelligence analyst Michael Dean wrote in a report on Tuesday.
European governments have been working to help the auto sector.
Germany on Tuesday said it would earmark billions of euros to support the development and production of climate-friendly cars. France is extending aid measures set up to help people buy new cars, while the Italian government is setting aside hundreds of millions of euros to support the sector.
PSA Group has cut production at several French factories after the nation's lockdown forced dealerships to close and led to a collapse in orders. The lobby group La Plateforme Automobile warned earlier this month that if showrooms cannot reopen quickly, the industry faces even worse consequences than this spring.
France and the UK locked down late last month and in early November, shutting car showrooms and pressuring sales further.
Europe's five largest markets all posted negative results in October. Sales in Spain fell by 21 percent and by 9.5 percent in France, while Italy, Germany and the UK registered more moderate drops of 0.2 percent, 3.6 percent and 1.6 percent respectively.
Reuters and Bloomberg contributed to this report