The storms are expected to last through at least Wednesday in Beijing, neighboring Tianjin and a swath of north China stretching from Jilin province in the northeast through Inner Mongolia to Xinjiang in the desert northwest, the China Daily and other media said.

That region is home to hundreds of millions of people.

More storms were expected later in the week in Xinjiang and other parts of the northwest, according to news reports.

Windborne dust from China's northern plains often blows as far as South Korea and Japan and sometimes crosses the Pacific Ocean to reach California.

Japan's national Meteorological Agency said the dust has reached the country's north and west and warned of reduced visibility, but didn't say any health effects were expected.

In Beijing, a doctor in the respiratory ward of Chaoyang Hospital, one of the capital's biggest, said the number of patients with breathing problems Monday was two to three times normal. He refused to give his name or any other details.

Commuters wore surgical masks or wrapped their heads in scarves as protection against the dust.

China's government has been replanting "green belts" of trees throughout the north in an effort to trap the dust after decades when the storms worsened amid heavy tree-cutting.

Last week, the western Xinjiang region was hit by its worst sandstorm in decades, which killed one person and left thousands stranded after sand covered railways and high winds smashed train and car windows.