"Earlier this evening a suspicious package was left unattended at the front gate," the tournament said in a statement. "For the safety of the public the Miami-Dade police have set up a perimeter and cordoned off the area until the package can be secured.
"We apologise for the inconvenience but the safety of the public must be placed first."
As world number one Serena Williams was playing fifth seeded German Angelique Kerbrer in a quarter-final on centre court, word began to filter through the complex that people were not being allowed to exit the facility.
Local news reports also said that four-lane traffic was halted in both directions in front of the complex while spectators were prevented from entering.
World number one Rafa Nadal was playing the final match of the evening session against Italian Fabio Fognini and was expected to go ahead as scheduled.
Security has been beefed up around major North American sporting events since last year's Boston marathon bombings left three people dead and wounded 264.
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- Serena Williams
- suspicious package