Another crease in China-Japan relations is seen as the irritating China smog now blankets Japan.

The month-long smog hanging over China had been blown over to Japan's skies, putting another strain to the relations of the two countries riled by a diplomatic rift over coveted Senkaku Islands.

"China is our neighbour, and all sorts of problems happen between us all the time," Takaharu Abiko was quoted by the AFP. "It is very worrying. This is dangerous pollution, like poison, and we can't protect ourselves. It's scary."

Although the Ministry of Environment of Japan expect the weather to improve by Wednesday, with the smog blowing from Beijing to slowly if not totally recede, it advised residents in the west of Japan to continue to wear masks and close their windows.

Atsushi Shimizu, from Japan's National Institute for Environmental Studies (NIES), confirmed the particulate matter contained in the toxic smog pollution hovering in the country's air zone, recorded at 50 microgrammes, is well above government-imposed limits of 35 microgrammes.

Authorities initially thought the cause of the hazy weather was the yellow sand from desert regions of Mongolia.

But "at this time of year they are definitely not yellow sands, so they're toxic particles," Shimizu said. He advised people "with respiratory diseases should be careful."

"Access to our air-pollution monitoring system has been almost impossible since last week, and the telephone here has been constantly ringing because worried people keep asking us about the impact on health," an environment ministry official said.