BEIJING (AFP) -- Hugo Barra, who caused a sensation in 2013 by leaving Google to become a vice president of Chinese smartphone maker Xiaomi, announced Monday he was returning to the United States for health reasons.

Barra, under whom Xiaomi was for a time China's best-selling brand, described his experience as a "spectacular" journey but said it was time to return home for a "new adventure". He did not elaborate.

"But what I've realized is that the last few years of living in such a singular environment have taken a huge toll on my life and started affecting my health," he said in a message on Facebook, without giving details.

Beijing and other Chinese cities are notorious for dangerous air pollution.

"My friends, what I consider to be my home, and my life are back in Silicon Valley, which is also much closer to my family," he said.

Barra said Xiaomi was now well placed to continue its international expansion.

The firm, created in 2010, was little known outside China when it recruited Barra to run its international activities.

The highly publicised recruitment marked the beginning of its dramatic transformation into an industrial giant. It briefly held the top slot for smartphone sales in China, far ahead of Apple and South Korea's Samsung.

At Barra's instigation, Xiaomi also made some overseas breakthroughs, notably in Southeast Asia, Russia, and especially India -- where he achieved $1 billion in annual revenue.

Despite his efforts, Xiaomi still depends on the Chinese market for the overwhelming majority of its sales.

But it faces strong domestic competition -- including newcomers Oppo and Vivo -- in the low-cost smartphone niche, and its market share continues to decline.

In the third quarter of 2016, Xiaomi was fourth with 8.7 of the Chinese market compared to 16 percent a year earlier.

This was far behind Oppo and Vivo (about 17 percent each) and China's Huawei (15.7 percent), but just ahead of Apple and Samsung, according to IDC.