The 67-year-old Mukasey was delivering a speech to the Federalist Society at a Washington hotel when "he just started shaking and he collapsed," said Associate Attorney General Kevin O'Connor. "They're very concerned."
Later, a senior law enforcement official said Mukasey appeared to be talking when he was taken away. He was conscious during part of the ambulance ride to hospital, said the official, who spoke on condition of anonymity because he was not authorized to discuss the situation.
Mukasey, the nation's top law enforcement official, was 15 to 20 minutes into his speech about the Bush administration's successes in combatting terrorism when he began slurring his words. He collapsed and lost consciousness, said O'Connor, the department's No. 3 official, who was traveling at the time and was alerted to what had occurred.
Mukasey's was noticeably shaking during his speech before he collapsed shortly before 10:20 p.m. EST. His security detail called 911.
Mukasey was on the stage for 10 minutes being attended to by his FBI detail before medics arrived, according to a Justice Department official who was there. Mukasey was still breathing at the time, said the official, who spoke on condition of anonymity because she was not authorized to talk to the media.
An FBI official said Mukasey got stuck on a word during his speech at the Marriott Hotel at Wardman Park in northwest Washington, repeated it several times and then "went down hard."
In the prepared remarks of his address to the conservative legal group, Mukasey planned to defend the Bush administration's "fundamental reorganization" of the government since the Sept. 11, 2001, attacks and policies put in place to detain terror suspects. He also was planning to talk about the continuing threat of al-Qaida.
President George W. Bush was informed about Mukasey's collapse, press secretary Dano Perino said.
"The president has him in his thoughts and will be kept apprised and hopes that he will be back up and at 'em again soon," she said.
Bush, a fierce loyalist, ventured outside his circle of friends and Texas associates to tap Mukasey 14 months ago as Gonzales' replacement. Gonzales, the president's longtime friend and fellow Texan, quit after months of senators' demands for his resignation and investigations that called his credibility into doubt.
In a sun-drenched morning announcement on the White House lawn, Bush introduced Mukasey as "a tough but fair judge" and asked the Senate to confirm him quickly.
"Judge Mukasey is clear-eyed about the threat our nation faces," Bush said, praising his reputation as a smart and strong manager.
Mukasey, the former chief U.S. district judge in the Manhattan courthouse just blocks from ground zero, earned a reputation as a tough-on-terrorism jurist with an independent streak.
As a judge, Mukasey ordered the detention of young Muslim men as so-called material witnesses in terrorism cases following the Sept. 11 terror attacks. While those decisions drew sharp criticism from immigration lawyers, Mukasey won praise from Bush administration lawyers.
Mukasey endorsed much of the USA Patriot Act, which Bush pushed through Congress following the terror attacks to secure broad new law-enforcement power.
And yet he once criticized the Bush administration from the bench for overstepping in a terrorism case. As a jurist, he was known for his brusqueness and impatience with people who waste his time.
Before joining the administration, the former judge was a partner at New York-based law firm Patterson Belknap Webb & Tyler.