Merseyside Police have seized three drones after they were flown in restricted airspace over the Grand National racecourse at Aintree.
The operators were located and the aircraft seized, while another operator was given "advice".
Chief Inspector Iain Wyke, in charge of the policing operation for the event, said: "This incident demonstrated the excellent detection work by officers who were able to swiftly identify the operators and seize the equipment.
"Please be mindful that airspace restrictions will remain in place for the duration of the event, and if we suspect a drone is being flown in the restricted area, then we will take action.
"If you commit an offence and fly a drone within the restricted area without permission, your equipment may be seized, and you may render yourself liable to prosecution."
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Police and organisers have introduced new security measures this year, with approximately 150,000 people descending on the site. More than 800m are expected to watch the festival on TV across the world.
Superintendent Matthew Moscrop, of Merseyside Police, said criminal activity "will not be tolerated". He continued: "As ever, we are expecting a large number of visitors to Aintree, and it is another prime opportunity to showcase what Merseyside has to offer. Anti-social behaviour, hate crime, disorder and other criminal activity will not be tolerated and will be dealt with robustly."
Large security cordons have been erected, it is understood, to help prevent security hazards. Plain clothes police officers will also be deployed at the event to monitor crowds
Last year, protestors attempted to glue themselves to a fence and hundreds more tried to get onto the racecourse to stop the race. It led to Merseyside Police making more than 100 arrests and was followed by further smaller protests during subsequent weeks.
On Friday, three men were arrested following reports of a fight at Aintree's Ladies Day.
The altercation was reported as racegoers enjoyed the second day of the Randox Grand National Festival at the Liverpool Racecourse.
A Merseyside Police spokeswoman said: "Three men have been arrested on suspicion of affray following a report of a fight at the front of the Princess Royal Stand today."
The force said the report, of an altercation involving four or five men, was made at 2.25pm.
One man received treatment on site for minor injuries, the spokeswoman said.
