An armed man has been shot dead after entering the secure perimeter of US President Donald Trump's Mar-a-Lago residence in Florida, the Secret Service has said.

The man was carrying a shotgun and fuel can when he was stopped and shot by Secret Service agents and a Sheriff's deputy, authorities said.

The incident happened around 01:30 ET (06:30 GMT) on Sunday morning, when the president was in Washington DC. 

The suspect has been named as Austin T Martin of Cameron, North Carolina, according to the BBC's US partner CBS.

His family had reported him missing on Saturday, CBS reports.

Officials are looking into whether he bought the gun along the driving route he took from North Carolina to Florida, according to CBS.

Secret Service agents fired at him after they saw him "unlawfully entering the secure perimeter at Mar-a-Lago early this morning", agency spokesman Anthony Guglielmi posted on X.

The suspect "was observed by the north gate of the Mar-a-Lago property carrying what appeared to be a shotgun and a fuel can", the agency said in a statement.

The man was then shot after refusing orders, Palm Beach County sheriff Ric Bradshaw said.

"The only words that we said to him was 'drop the items' which means the gas can and the shotgun," Bradshaw told a news conference. 

"At which time he put down the gas can, raised the shotgun to a shooting position," he said. 

At that point, agents fired their weapons to "neutralise the threat", he said.

The officers were wearing body cameras and no law enforcement officers were injured, he added.

Bradshaw said that he does not know if the suspect's gun was loaded, and that will form part of an investigation, which the FBI will be assisting in.

Security at Mar-a-Lago is extremely tight, with an outer cordon of local Palm Beach sheriffs and an inner one maintained by the Secret Service. Visitors are searched, and cars and bags are swept by dogs and metal detectors.