(Changes slug, updates with lockdown lifted, reaction)
MIAMI, March 25 (Reuters) - The Sony Open in Miami was locked down while the bomb squad investigated a suspicious package on Tuesday, preventing thousands of spectators from entering or leaving the sprawling tennis complex.
The all clear was given at around 9:30 ET (0130 GMT), some 30 minutes after officials had confirmed the lockdown, allowing ticket holders to exit.
Local news reports had also said four-lane traffic was halted in both directions in front of the complex while spectators were prevented from entering.
"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."
Word first began to filter through that people were not being allowed to leave the facility as world number one Serena Williams was playing fifth seeded German Angelique in a quarter-final on centre court.
"Yeah, there was a bomb threat and a lockdown but that's all I know about it. Scary," said Williams after beating Kerber.
World number one Rafa Nadal was scheduled to play the final match of the evening session against Italian Fabio Fognini and the match went ahead as planned.
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. (Editing by Ian Ransom/Peter Rutherford)