A double-digit gain in North America failed to prevent world vehicles sales from falling below year-ago levels for the first time in eight months, WardsAuto data indicates.

Global auto makers delivered 6.87 million units in September, a 0.9% decrease from like-2011.

Positive economic signs, coupled with the drive to replace aging vehicles and growing credit availability, lifted sales 12.3% in the U.S.

Supported by gains of 6.5% in Canada and 9.1% in Mexico, North America’s 11.5% rise in volume made it the fastest-growing region in the world for the month and year-to-date, with sales outpacing the first nine months of 2011 by 13.6%.

Asia/Pacific deliveries rose nearly 1%, despite downturns in the region’s two largest markets.

In China, the world’s No.1 vehicle market, sales fell for the first time in five months, dipping 1.7% to 1.62 million. Political tensions with Japan may have contributed to the drop, with some Chinese consumers boycotting Japanese brands.

Deliveries dipped 3.4% in Japan, marking the market’s first year-over-year decline in 12 months.

Those losses were offset by considerable growth in two smaller markets: Indonesia, where sales rose 27.9%, and Thailand, where year-over-year deliveries jumped 52.7%. The Asia/Pacific accounted for 43.5% of monthly global vehicle sales. Year-to-date, volume in the region is up 10.3%.

In Europe, the ongoing sovereign-debt crisis continues to depress the new-vehicle market, where sales plunged 7.1% – the worst year-over-year decline since late 2009. That dropped year-to-date volume nearly 5% below like-2011.

Sales were down in every major market in the region except Russia (+9.0%), Turkey (+16.3%) and the U.K. (+7.3%). In September, the U.K. led all of Europe and was the world’s fourth-largest market, with reported sales of 404,000 units.

Deliveries in South America slipped 10%, to 460,000 units, accounting for 6.7% of worldwide sales for the month and giving the region a 7% share of year-to-date volume.

In Brazil, South America’s largest market, sales fell 7.9% after an announced end to special tax incentives on new-car purchases drove August volume to record highs. The incentive eventually was extended through October, but September demand suffered from pull-ahead sales the prior month.

To-date, South America deliveries are up 2.1% from like-2011.

September was the eighth consecutive month in which global sales exceeded 6 million units, bringing year-to-date volume to 61.4 million, up 5.5% above year-ago.

WardsAuto currently is forecasting 2012 world vehicle sales to reach 83.1 million units.

jsousanis@wardsauto.com