Only about 50 percent of volunteers picked to work at the Rio Games have been turning up to some venues, organisers have revealed.
The lowest turnout has been among those working on venue entrances, especially those who had to deal with angry fans in the first days of competition when slow security checks resulted in long queues.
"They were under a lot of pressure in the first two to three days," Rio communications director Mario Andrada says.
"Working long hours and there was the classic tension - guarding entrances where they had to say no to a lot of people."
Into the second week of the Games, organisers also believe some volunteers have been forced to return to their jobs or other activities or just believed their job had been done.
That has prompted officials to activate extra staff who were trained and uniformed but not originally allocated positions.
Before the Games about 240,000 people applied to work as volunteers in Rio, with organisers originally planning to engage about 70,000.
Funding cuts forced them to slash that number to about 50,000.
In the first week of the Games, the Brazilian labour ministry also raised concerns over working conditions for paid staff at Rio 2016.
It said it had identified problems with 6500 workers including a lack of food and water, inadequate rest breaks, and excessively long work hours.
The ministry called on organisers to fix the problems or face fines.