Prime Minister Malcolm Turnbull has been caught off-guard by a last-minute invitation to visit Washington from Barack Obama.

Mr Turnbull is currently in the Philippines for the Asia Pacific Economic Cooperation (APEC) summit, where he and the US president held a bilateral meeting.

While waiting for reporters to set up for a joint press conference after the meeting, it seems Mr Obama remembered he had not flagged an important invitation to his potential future guest.

Mr Obama: "One of the things I'm going to do is I'm going to announce that I'm inviting you to Washington." Mr Turnbull: "Sorry?" Mr Obama: "I'm going to say that I'm inviting you to Washington and I hope you can accept." Mr Turnbull: "That you're going to...?" Mr Obama: "Invite you to Washington." Mr Turnbull: "Oh yeah, good. For certain."

The president later went on to officially announce the invitation and the Prime Minister's acceptance.

Counter-terror and security had been the focus of the pair's first official bilateral talks at the summit, with leaders from more than 20 countries gathered in Manila for the economic forum.

Mr Turnbull is currently on the fourth part of his five-nation tour, having also visited Indonesia, Germany and Turkey for talks since flying out of Australia last Friday.