This is the most important story of my lifetime - I think it's our job to stay on air

NBC news president Neal Shapiro

"That combines aggressiveness in getting information out with the awareness that we should not be speculating and we should not be alarming people."

Some 79.5 million people watched the coverage on Tuesday night, according to Nielsen Media Research.

With many networks providing continuous coverage, there were many split-second decisions on what to show.

For example all networks had access to video depicting victims jumping from the building.

CBS showed the footage, and has defended its decision saying it was appropriate to the story. NBC and Fox News showed it once then pulled it.

Relatives were desperate for information from TV news

Most executives agree that providing coverage of such an attack poses serious dilemmas for TV executives.

"I don't think it's an easy call," said NBC news president Neal Shapiro.

Shapiro said that another issue is the need to separate Islam from extremism, even if some of the religion's believers masterminded the attack.

US stations ABC, CBS, NBC and cable news networks are providing continuous coverage which may continue beyond Friday.

"This is the most important story of my lifetime," said Shapiro. "I think it's our job to stay on air."

Providing such immediate coverage means there were a few mistakes.

Many networks are showing continuous coverage of the rescue

There were reports that as many as 800 people died at the Pentagon, when the estimate is now 190.

There were also wildly different figures for the numbers working at the World Trade Center or likely to be in the building at the time of the attack.

It was the 24-hour news network CNN from Atlanta which was first to begin coverage at around 1350 BST.

But struck with the horror of the story, there was none of the "first off the block" triumphalism usual from news networks under similar occasions.

Most of the US news networks were said to have been sharing footage.

"I think everybody has been using the proper tone and have been cooperative with one another in making sure information gets out," said CNN chairman Walter Isaacson.

"We know this is larger than a typical story."