An investigation is underway at President Donald Trump's Mar-a-Lago resort, police said.

Palm Beach Police swarmed the resort in a "possible trespassing", news organisations reported.

"There's an ongoing investigation right now, and we're working on it," said Michael Ogrodnick, a spokesman for the Palm Beach Police Department, when asked whether police had responded to a Mar-a-Lago trespassing complaint.

"We will let you know as soon as we have something, which should be soon."

Police haven't released any information other than they are working an open investigation.

Security breaches have happened before at Mar-a-Lago, raising fears of potential national-security threats.

Earlier this year, federal authorities arrested Yujing Zhang, 33, for unlawfully entering the club.

Zhang, a Chinese national, was convicted of entering a restricted area and lying to a federal agent.

The Secret Service originally said she was carrying a thumb drive loaded with "malicious malware," but Zhang did not face any espionage-related charges. She currently awaits deportation.