An appeals court has upheld a decision barring the US government from requiring tobacco companies to put large graphic health warnings on cigarette packages to show that smoking can disfigure and even kill.

The US Court of Appeals in Washington on Friday affirmed a lower court ruling that the requirement ran afoul of the US Constitution's free speech protections.

Some of the nation's largest tobacco companies sued to block the Food and Drug Administration (FDA) mandate to include warnings to show the dangers of smoking.

They argued that the proposed warnings went beyond factual information into anti-smoking advocacy.

The government argued the photos of dead and diseased smokers are factual in conveying the dangers of tobacco, which is responsible for about 443,000 deaths in the US a year.

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The nine graphic warnings proposed by the FDA include color images of a man exhaling cigarette smoke through a tracheotomy hole in his throat, and a plume of cigarette smoke enveloping an infant receiving a mother's kiss.

These are accompanied by language that says smoking causes cancer and can harm fetuses. The warnings were to cover the entire top half of cigarette packs, front and back.

In recent years, more than 40 countries or jurisdictions have introduced labels similar to those created by the FDA.

The World Health Organization said in a survey done in countries with graphic labels that a majority of smokers noticed the warnings and more than 25 per cent said the warnings led them to consider quitting.

Tobacco companies increasingly rely on their packaging to build brand loyalty and grab consumers, one of the few advertising levers left to them after the government curbed their presence in magazines, billboards and TV.

Free speech

"It's a significant vindication of First Amendment principles," Floyd Abrams, an attorney representing Lorillard Tobacco, said referring to the US Constitution's free speech guarantee.

"There's never been any doubt that the government could require warnings on products that can have dangerous results," Abrams said

"And what the court is saying is that there are real limits on the ability of the government to require the manufacturer of a lawful product to denounce the product in the course of trying to sell it."

The FDA declined to comment on pending litigation, and the Justice Department said it would review the appeals court ruling. Public health groups are urging the government to appeal.