Barack Obama
President Obama boards the helicopter to Camp David (Reuters)

President Barack Obama celebrated his 52nd birthday on Sunday surrounded by friends at his Camp David retreat.

Obama kicked off his weekend on Saturday with a round of golf at Joint Base Andrews with friends from his childhood home of Hawaii, Chicago, where he lived before becoming president, as well as aides past and present.

It is reported that the winners of the game got to join Obama in the presidential helicopter while the losers had to take a long car ride to the retreat, in the Catoctin Mountains, Maryland.

Among those who played were two Chicago friends, Marty Nesbitt and Eric Whitaker, and high-school friends, Mike Ramos and Bobby Titcomb.

Former aide Reggie Love, nicknamed Obama's "body man" before he left the White House to begin an MBA, also played, as did Chicago chef Sam Kass, who has also served as a White House chef, senior policy adviser on nutrition, and executive director of Michelle Obama's Let's Move! campaign.

Michelle Obama is believed to have travelled separately to Camp David.

However, the day is not believed to have been spent simply relaxing, with the president receiving regular updates on the terrorism threat that prompted the US to close 21 of its embassies.

Obama is scheduled to fly back to the White House on Sunday. His diary this week includes an appearance on the Tonight Show with Jay Leno, a trip to the West Coast to discuss plans to help homeowners, and a visit to troops at Camp Pendleton.

He is also due to meet Greek Prime Minister Antonis Samaras on Thursday.

Last week, House Democrats presented Obama with a birthday cake when he visited the Capitol, and American Legion youth members sang "Happy Birthday" to him during a White House visit late last month.

In recent weeks, Obama has focused on the policies observers believe the president wants to define his second term, including economic policies designed to help the American middle class, and rolling out his healthcare programme.