The US added a disappointing 136,000 new jobs in September as signs of a slowdown in hiring appeared to mount. But the unemployment rate ticked down again to a 50-year low of 3.5%.

Economists had predicted the US would add 145,000 jobs over the month. The American jobs market is experiencing its longest growth streak on record – 108 months of gains in a row – and the unemployment rate is the lowest since December 1969. But the rate of growth is slowing markedly.

The economy added 130,000 jobs in August and has gained an average of 161,000 a month this year. Last year, the US added an average of 190,000 jobs a month. The growth rate is still comfortably ahead of the 100,000 a month that economists estimate the US must add to sustain a health jobs market.

The figures come as global stock markets have been rattled by signs of slowing economic growth and an escalation in the trade disputes between the US and the European Union.

Investors took flight on Wednesday when ADP, the US’s largest payroll supplier, released its latest survey of private sector hiring. ADP said 135,000 new jobs were added in September, not far from analysts’ expectations, but it cut the previous month’s figures and warned that growth was slowing.

“Businesses have turned more cautious in their hiring,” said Mark Zandi, the chief economist of Moody’s Analytics, which helps compile the report. “Small businesses have become especially hesitant. If businesses pull back any further, unemployment will begin to rise.”

The latest government figures underline the weakness in manufacturing, which has been hurt by the US’s trade disputes with its largest economic partners. Hiring in manufacturing fell slightly in September. But the biggest loser was retail, once one of America’s largest employers. About 11,000 jobs were lost in retail over the month.