China's leading e-commerce retailers have warned their supplies of air purifiers are dwindling after sales skyrocketed in recent days as heavy smog and haze hit large parts of Central and East China.

A child with device to help breathe clean air is seen in hospital waiting for treatment for cough caused by severe air pollution in Beijing on Jan 14, 2013. [China Daily]

Most air purifiers at gome.com.cn, one of China's leading e-commerce sites, were sold out by Monday, with only one model, priced at 999 yuan ($161) after discounts, still available.

"We started to run out of stock on Sunday night because orders for air purifiers suddenly flooded in," said Peng Liang, a Gome spokesman.

Air purifier sales are up at least 700 percent compared with the same period in previous years, he said, with Beijing residents placing the most orders.

Purifiers priced around 2,000 yuan have been the most popular, he said.

Air purifiers were also a hot item at the Beijing-based 360buy.com, another e-commerce site. According to the website, sales on Saturday and Sunday were more than triple the sales in the first 10 days of this month.

Air purifier sales in Beijing on those two days were six times higher than in the first 10 days of January.

Suning.com, another major e-commerce company, has not released its air purifier sales figures, but marketing manager Chen Gongjing said there were more than 30,000 searches on the site for purifiers on Monday morning, about three times more than normal - searches for face masks were also three times the normal rate.

Mo Daiqing, an e-commerce analyst at research company China e-Business Research Center, said online companies are usually prepared for sales or promotions in terms of stock.

But in this case, the companies were taken by surprise by the large number of orders.

"In the past, only people refurbishing their apartments would buy air purifiers, and the number of them used to be quite small," said Peng with Gome.

"There has been similar weather before, but the haze lasted only about one day at the most. The smog has never been as serious as this," he said.

He expected the depleted stock of air purifiers will be replenished by Tuesday at the earliest.

Mo warned that despite the spike in sales, there might be after-sales issues such as cancellation of orders and delayed arrival of products.