CNN

President Bush underwent a colonoscopy Saturday morning.

WASHINGTON (CNN) - President Bush on Saturday transferred his presidential power temporarily to Vice President Cheney just before he underwent a routine colonoscopy.

"This morning at 7:16 a.m., letters from President Bush were faxed to the Speaker of the House and President Pro Tempore of the Senate," the White House announced. "These letters informed them of his decision to invoke Section 3 of the 25th Amendment to voluntarily transfer his powers and duties to the Vice President. This transmission transfers his duties, therefore the Vice President is now serving as Acting President."

The White House said the "transfer ends when the president transmits a second "written declaration" – i.e., a letter – to the congressional leaders advising that he is resuming those powers effective immediately."

The procedure, called "routine" has already begun, the White House said.

It is expected to take about two and a half hours, the chief White House spokesman said on Friday.

Tony Snow said Friday that the procedure, during which a doctor looks for any signs of cancer, was to be carried out at Camp David, Md., and the president would be placed under anesthesia.

Bush's last colonoscopy was in June 2002, and no abnormalities were found, Snow said.