The fire, which started in the early afternoon local time, was quickly controlled by firefighters, G1 reported citing Rio de Janeiro's fire department.
There was no damage to Olympic facilities and no injuries at the site, which is still under construction ahead of the planned Aug. 5 opening of the games. The shipping container held construction supplies.
Rio de Janeiro officials believe the fire may have been intentionally set by the protesters who held a demonstration outside the site earlier, G1 reported.
The unemployed workers allege they were laid off in December but have yet to receive their last month of salary or their legally required severance payments, G1 reported.
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The fire, while small, highlights the increasing risk organizers face as the clock ticks down to the planned opening of the games seven months from now.
Deadlines for the completion of the Olympic sporting facilities have been repeatedly missed and many related projects have been scaled down or scrapped from the original bid-winning proposal.
Even if completed before the games start, some delayed facilities may not be able to be tested before official competition.
During the 2014 World Cup in Brazil, which also faced delays and saw key infrastructure projects unfinished in time for the event, a partly built overpass collapsed in Belo Horizonte, Brazil, one of the host cities.
(Reporting by Jeb Blount; Editing by Bill Trott)
