A gunman has been shot dead after entering US President Donald Trump's Mar-a-Lago estate in Florida, the National Security Agency has said.

Authorities’ say the man was armed with a gun and a gas can when he was stopped by security guards.

The incident occurred on Sunday morning, while the president was in Washington, DC.

BBC US partner CBS has identified the suspect as Austin T. Martin, who was born in Cameron, North Carolina.

Moore County Police told the BBC that his family in North Carolina had reported him missing on Sunday morning.

Police have since turned over the missing person's information to federal authorities, police said.

Police said they had no prior knowledge of Martin and that he was not involved in the ongoing investigation in Florida.

Authorities are investigating whether he purchased the gun while traveling from North Carolina to Florida, CBS reported.