Although they say those who fell ill in Jilin could have been poisoned, psychogenic experts outside China say it is also possible for some to have been affected by toxic fumes while others exhibited psychosomatic illnesses set off by real poisonings.

Robert E. Bartholomew, a sociologist at the International University College of Technology in Malaysia, said the government’s handling of the episode, including the ban on reports in the news media, might be fueling paranoia. “The best way to handle psychogenic illness is to be open and transparent, which tends to dissipate concerns,” said Mr. Bartholomew, a co-author of “Outbreak! The Encyclopedia of Extraordinary Social Behavior.” If it is indeed a case of mass hysteria, he said, it would be the largest instance of workplace psychogenic illness on record.

The episode is not Jilin’s first experience with the perils of aniline. In 2005, an explosion at another factory that produced the volatile substance killed eight people and sent 100 tons of deadly benzene and nitrobenzene into the Songhua River, tainting drinking water for millions of people downstream.

Public anxiety was high even before the new $125 million aniline plant opened in early April. During a test run last September, two security guards standing in front of the textile plant were overcome by fumes. Connell paid them compensation, although it is unclear what adjustments were made to the manufacturing process and, more important, the venting of its airborne byproducts, a mix of carbon monoxide, hydrogen sulfide and nitrogen oxide.

Shortly after production began, Li Hongwei, a 34-year-old Connell worker, collapsed and died on the job. Although rumors suggested that he had been poisoned, factory officials insist that Mr. Li succumbed to a heart attack. His family, which received a compensation package that included a job for his wife and a monthly $200 stipend for his mother and son, declined to talk to reporters.

After Mr. Li’s death, the authorities forced Connell to halt production for a month. But in early June, not long after it resumed, Wang Shulin, a 38-year-old technician at the textile mill, went into convulsions while on the job. He was sent to the hospital but died just as doctors were administering a CT scan, according to co-workers. The cause of death was a brain hemorrhage.

Image Textile workers were stricken in the industrial city of Jilin. Credit... The New York Times

Factory officials insist that Mr. Wang’s death had nothing to do with chemical exposure.

Such assurances have done little to quiet fears that Connell continues to taint the air. Li Jingfeng, 35, an electrician at an ethanol plant that abuts the aniline plant, said chemical detectors at his factory had gone off five or six times in the last month, forcing workers to evacuate. “Everyone is nervous about what’s coming out of that place,” he said.