Toyota kept the title of world's biggest automaker on Thursday with first-quarter sales of 2.52 million vehicles globally, outpacing Volkswagen and General Motors, despite weakening demand at home.

The Japanese giant's numbers, down 2.5 percent from a year ago, come after the German automaker earlier said it moved 2.49 million vehicles in the quarter, while US-based GM shifted 2.4 million units, both up from a year earlier.

Toyota expects sales this year to slip to 10.15 million from a record 10.23 million vehicles in 2014, owing to a shaky outlook for Japan, concerns about a China slowdown and as it beefs up its focus on quality after a string of safety scandals.

That means Volkswagen could shift into pole position as the German automaker rides momentum in emerging economies that could see it take the lead in global auto sales for the first time in 2015.

Camry and Prius maker Toyota broke GM's decades-long reign as the world's top automaker in 2008 but lost the crown three years later as Japan's 2011 earthquake-tsunami disaster hammered production and disrupted the supply chains of the country's automakers.

However, in 2012 it once again overtook its Detroit rival, which sells the Chevrolet and luxury Cadillac brands.

Thursday's sales figures come a week after Toyota ended a freeze on building new factories by unveiling plans for a $1.0 billion plant in rising industry power Mexico and another production line in China

The Japanese carmaker began operating a new Thai plant in 2013, but since then it has halted investment as the global car market struggled with oversupply and weak demand.

Despite the expansion, Toyota chief Akio Toyoda said his family firm would not embark on unrestrained expansion, as it overhauls its production methods to slash development costs.

While the car giant is set to log a record $18 billion fiscal year profit next month, largely due to a weak yen and strong North American sales, Toyoda said the company must do more to protect its bottom line in a fast-changing market.

"An increase in production does not mean an undisciplined pursuit of more," he said.

Toyota, among other major automakers, has been struggling to recover a reputation for safety after the recall of millions of cars around the world for various problems, including an exploding air bag crisis at supplier Takata.

There are also growing fears about the entire industry's prospects in China owing to concerns about the health of the world's number-two economy.

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