WATCH: Obama puts Trump in his place right before his big speech
US President Barack Obama holds a press conference following the conclusion of the Association of Southeast Asian Nations (ASEAN) summit in Laos on September 8, 2016 (AFP Photo/Saul Loeb)

U.S. President Barack Obama on Friday said he had better things to do than comment on Republican presidential candidate Donald Trump's announcement about the so-called birther question over Obama's citizenship.

"I'm shocked that a question like that would come up at a time when we've got so many other things to do - well, I'm not that shocked actually," Obama told reporters.

"I was pretty confident about where I was born. I think most people were as well," Obama told reporters in the Oval Office, where he was meeting about a trade deal with Asia.

Trump plans to address Obama's citizenship on Friday, a day after he refused in a newspaper interview to say whether he believed Obama was born in the United States.

"My hope would be that the presidential election reflects more serious issues than that," said Obama, who several years ago released a longer version of his birth certificate to answer those who suggested he was not U.S. born.

(Reporting by Roberta Rampton; Editing by Alistair Bell)