China's crude steel output may fall for the first time in 31 years this year, a senior industry analyst said Monday in a report also published on the state-backed China Iron and Steel Association's website.

China is the world's largest steel producer, accounting for half the world's output and serving as a bellwether for the pace of construction activity and global industrial demand.

"A significant decline in China's second-half steel output is a foregone conclusion," Xue Heping, senior analyst for China's Steelinfo consultancy, told Dow Jones Newswires.

Mr. Xue's projection, which he said was based on weaker macroeconomic conditions and steel demand, marks a three-decade turning point in China's heavy industry and may reverse gains in imports of coking coal and iron ore, which are used to make steel.

China's economy grew 7.6% in the second quarter compared with a year earlier, the slowest rate since the global financial crisis. The slowdown has fueled a surge in Chinese net steel exports, which reached their highest levels in two years in May and June, as steelmakers have tried to export their way out of waning domestic demand. It isn't clear yet if Chinese production will fall to the degree that it undercuts the export surge. U.S. analysts fear that mills are instead trying to use the U.S. market as an escape valve for products it can't move at home.

Crude steel production may reach 678.68 million metric tons this year, a 0.7% decline from 2011, when China produced a record 683.27 million tons, Steelinfo said.

Production cuts since June have been widespread among larger Chinese steelmakers, said Mr. Xue, a former analyst for CISA of 30 years' standing whose reports are circulated to the National Development and Reform Commission, Beijing's top economic planning agency.

Total output had been cut by 2 million tons as of last week compared with the start of July, he said. On an average daily basis, crude steel output fell to around 1.95 million tons last month compared with 2 million tons in May and June, Mirae Asset Securities said in a report last week.

CISA's larger member-mills have led the output suspensions, though smaller steelmakers are following suit, Mr. Xue said.

Second-half output may decline around 10% compared with the first half, Steelinfo said. In the first six months this year, China produced 357 million tons of crude steel, up 1.8% on year—the smallest magnitude rise in 30 years, Mr. Xue said. Since the global financial crisis, China's steel output in the second half has fallen compared with the first half, largely because of a summer lull.

"As steel prices fall, the pressure to cut production has only grown," he said. Steel futures on the Shanghai Futures Exchange have fallen by around 13% so far this year. Steelmakers' profits fell 95.8% on year in the first half, CISA said last week.