There are two levels of security at the stadium, managed by the Secret Service and the Transportation Security Administration (TSA).
The latter is typically responsible for security at US airports, with fans and media having to pass through airport-style scanners.
One member of the media said that when they arrived at the entrance, they were told to stand in another line because there were no security dogs at that gate to search bags.
World Cup volunteers at the stadium told BBC Sport that the number of people turning out well in advance of the game was much higher than for the previous seven matches at the stadium.
Gates opened to fans at 11:00 local time – four hours before kick-off – and new gates were opened from time to time to reduce crowding.
At this stage it is not anticipated that there will be any delay in the start of the match or any other disruption to the match.