The heavy smog shrouding northern China may have ignited public anger about the country's pollution, but it appears not everyone is a loser.

Sales of face masks and air purifiers have risen in tandem with pollution levels in Beijing, which remained at hazardous levels in many parts of the capital yesterday.

Even sales of condoms, sportswear and sport utility vehicles have benefited, according to the latest consumer figures, as Beijing's first pollution "red alert" entered its second day.

"What do you do when the smog forces you to stay home? Shop online," noted Chinese website efu.com, which collates consumer and fashion news.

Searches for face masks and air purifiers on the popular Taobao e-commerce platform surged by 142 per cent and 51 per cent respectively over the last 30 days, according to data published by the website.

A shop owner at Taobao told state news agency Xinhua that his shop has sold all imported air purifiers in stock. "We normally sell 20 to 30 purifiers a month," he said. "But we have sold over 80 just this week. I have sold out of all my stock."

The report said parents have even banded together to buy high-end purifiers for their children's classrooms because "too many kids fell ill during the recent smog".

More curiously, however, sportswear and condoms became top search items on Taobao as well, said efu.com, overtaking traditionally popular items like women's clothing and make-up.

With cities that suffered more serious smog recording more searches for sportswear, it is suggested that this is because people are preparing to exercise once the air quality improves. As for condoms, it could be due to women not wanting to get pregnant during polluted spells.

Separately, the heavy smog had also prompted an unlikely spike in vehicle sales, Bloomberg reported.

Car sales saw the biggest gain in nine months, according to the China Passenger Car Association.

"Those with children are more inclined to buy cars, given the perception that the air inside a vehicle is cleaner," it said in a presentation.

The sales increase in certain sectors contrasts with the losses suffered by some factories, which have been ordered shut for three days because of the red alert issued on Monday.

Local reports said the authorities have been vigilant and acted against polluters who flouted bans.

On Tuesday, Beijing's environment protection bureau inspected close to 600 pollutant-discharging factories and found 38 of them did not abide by the suspension order.

It also caught more than 3,000 cars breaching restrictions. Cars with odd-numbered licence plates were barred from Beijing's roads on Tuesday as part of measures to reduce pollution. Regulators were quoted as saying their workload tripled following the red alert.

Customs officers in Shanghai have also discovered 120,000 fake 3M respiratory masks, China News Service reported.

Pollution red alerts have been raised in more cities, the China Daily reported yesterday. Dingzhou and Xinji, two cities in Hebei province, which surrounds Beijing, issued their first red alerts.

The air in Beijing is expected to clear up today, but heavy smog is forecast to return by Saturday.