"The longest distance in the world," according to one joke making the rounds, "is not between life and death, but when I hold your hand at a crossing in Beijing and I can't see your face."

As with many of the country's more solemn situations, the choking smog blanketing Beijing since Monday has evoked wisecracks from social media users.

In the past few days, jokes on the topic have become one of the most discussed threads on China's largest micro-blogging site, Sina Weibo.

But despite the lighthearted approach to the pernicious atmosphere, the capital's residents are feeling the impact of what is the most severe bout of smog in Beijing since July.

The National Meteorological Center upgraded Tuesday's "yellow" alert to "orange", the second highest after "red", on Thursday afternoon as the smog worsened. On Friday, it continued to issue the orange alert and predicted that the smog covering much part of northern China will continue until Saturday night, when a strong wind blowing from the north might disperse the haze. It suggested that people stay indoors and wear masks if going out.

Dou Chen returned from the United Kingdom to China in February. Since coming home, she has suffered from a nettle rash for five months. A blood test found that she is allergic to substances in the air.

"When I travel outside Beijing, my symptoms are relieved," she said. But in the past two days, the rash worsened.

At Guang'anmen Hospital, a doctor told her the symptoms were connected to the smog.

A staff member with Beijing Children's Hospital who requested anonymity told Xinhua that, although the hospital hasn't seen an obvious rise in patient numbers yet, since heavy smog days have just begun, staff members were told to prepare for a peak in respiratory problems.

Wang Xia, 34, is a teacher with the No 25 Middle School. "Whenever persistent smog occurs, more students ask for sick leave," she said. "In a class with about 40, once more than 10 students left in the afternoon."

The environmental watchdog in Beijing blamed farmers who are burning fields of straw for causing the smog, which some Beijingers doubt.

Li Lixin, an air pollution treatment official with the Beijing Environmental Protection Bureau, said a satellite test conducted during the summer of 2013 showed a discharge from widespread straw fires could drive up the PM 2.5 reading in Beijing from 110 to 460 micrograms per cubic meter in a few hours.

Still, Web users questioned whether farmers are to blame.

"Agriculture has been a vital industry in China for hundreds, if not thousands, of years, and it is the tradition in rural areas to burn straw after autumn harvest and plow to bury the ashes in the ground as fertilizer," said a Weibo user nicknamed Sunflower. "But why didn't we have smog in the past?"

At such criticism, Wang Yu, head of the energy ecology department of the Beijing Agricultural Bureau, conceded that pollutants are mainly from motor vehicle exhaust, coal burning, industrial production and dust, rather than burning straw.

"But this is the season for burning straw, coinciding with a special climate that features high humidity and lack of wind," he said. "It was like the straw that breaks the camel's back, worsening the air pollution."

Beijing and its surrounding provinces have banned straw burning. But anti-smog measures didn't stop there.

The city also pledged to replace coal with cleaner-burning energy like electricity and natural gas for domestic use. It also hopes to curb coal sales and use by the end of 2020, as well as other high-pollution fuels, such as fuel oil, petroleum coke, combustible waste and some biomass fuel.

Beijing also raised the discharge fees this year for major pollutants such as sulphur dioxide and nitrogen oxide.

Li Lixin noted that it might take time to see the results of such measures. However, the government has attached great importance to the issue, and people's awareness of environmental protection has improved, Li said.

In the meantime, Beijingers are avoiding the outdoors and spending money to protect themselves indoors.

An old man surnamed Cheng said his friends with asthma and bronchitis remind each other not to go out on smoggy days.

Wang Xia's school has stopped outdoor activities for students. "What if we could have air cleaners installed in each classroom?" she said.

According to a sales representative, surnamed Zhang, for electrical appliance brand Sharp, sales of air purifiers almost doubled in the past two days on JD.com, an e-commerce platform.

Wang Qian and Wang Xiaodong contributed to this story.