LOS ANGELES - Former US president George W. Bush says his apparent lack of reaction to the first news of the Sept 11, 2001, attacks was a conscious decision to project an aura of calm in a crisis.

In a rare interview with the National Geographic Channel, Bush reflects on what was going through his mind at the most dramatic moment of his presidency when he was informed that a second passenger jet had hit New York's World Trade Center.

Bush was visiting a Florida classroom, and the incident, which was caught on TV film, has often been used by critics to ridicule his apparently blank face.

"My first reaction was anger. Who the hell would do that to America? Then I immediately focused on the children, and the contrast between the attack and the innocence of children," Bush says in an excerpt of the interview shown to television writers on Thursday.

Bush said he could see the news media at the back of the classroom getting the news on their own cell phones "and it was like watching a silent movie".

The former president said he quickly realized that a lot of people beyond the classroom would be watching for his reaction.

"So I made the decision not to jump up immediately and leave the classroom. I didn't want to rattle the kids. I wanted to project a sense of calm," he said of his decision to remain seated and silent.

"I had been in enough crises to know that the first thing a leader has to do is to project calm," he added.

The National Geographic Channel will broadcast the hour-long interview on Aug 28 as part of a week of programs called Remembering 9/11 on the cable network to mark the 10th anniversary of the attacks.

The interview was recorded over two days in May, without any questions being submitted in advance, the channel said.

National Geographic said Bush gives "intimate details" of his thoughts and feelings in a way never seen before.

Most of the interview is about the first minutes and hours of the day that Islamic militants hijacked four planes and crashed into the World Trade Center and the Pentagon.

Executive producer and director Peter Schnall said Bush, who has adopted a low public profile since leaving office in January 2009, brought no notes to the interview.

"What you hear is the personal story of a man who also happened to be our president. Listening to him describe how he grappled with a sense of anger and frustration coupled with his personal mandate to lead our country through this devastating attack was incredibly powerful," Schnall said.

US television networks are planning a slew of specials to mark the 10th anniversary of the Sept 11 attacks.

Those on National Geographic also include a documentary on the continuing US war on terror, and stories of ordinary people on Sept 11, 2001.

Reuters