Business activity in the UAE and Saudi Arabia dropped last month as seasonal factors and deteriorating global growth hit Gulf economies.
HSBC's headline purchasing managers index (PMI) in the UAE fell the most since the survey began. Output, employment and new orders all slowed. In Saudi Arabia, the index dropped to an 18-month low.
The bank said, however, that seasonal factors such as Ramadan and the summer holiday may mean the decline has been overstated.
Simon Williams, chief economist of HSBC in the Mena region, said: "You can't help feeling the slowdown across developed and emerging markets is evident here," he said. "This is the second or third month on month decline in the UAE and you have to come to the conclusion that the numbers are strongly suggesting the boost in the first half of the year is dissipating."
Signs of slowing growth are emerging in the economies of the US, Europe and China. From jobs growth in the US grinding to a halt to weak manufacturing data in the euro zone, major economies have been cooling in the second half of the year.
PMI data is an important gauge of activity in the services and manufacturing sectors of an economy.