Apple chief executive Tim Cook publicly came out as gay, saying in a magazine article that he wanted to support others who find it difficult to reveal their sexual orientation.

"So let me be clear: I'm proud to be gay, and I consider being gay among the greatest gifts God has given me," Cook said in an article he wrote in Bloomberg Businessweek published on Thursday.

"I don't consider myself an activist, but I realise how much I've benefited from the sacrifice of others," he said.

Cook's admission makes public a fact long known but rarely discussed openly in California's close-knit Silicon Valley technology community.

A popular gay and lesbian magazine, Out, placed Cook at the top of its annual top 50 list of gay people in 2013.

While never broadcasting his sexual orientation, Cook has frequently spoken out against discrimination of the lesbian, gay, bisexual and transgender (LGBT) community, most recently this month when he addressed a group in his native Alabama.

Now, he is at least the third CEO of a publicly listed US company to come out of the closet.

C1 Financial's Trevor Burgess and IGI Laboratories' Jason Grenfell-Gardner have previously acknowledged that they are gay.

Cook's disclosure was greeted by a flood of congratulatory comments on Twitter.

"I have so much respect for this man," a person identifying himself as Andrew Clarke tweeted.

The fact the chief executive of the biggest US publicly traded company felt he could disclose his sexual preference in such a public way, and with the backing of his chairman, shows how times have changed in the past few years.

BP chief executive Lord Browne, who kept his sexual orientation secret for decades, was forced to come out after a boyfriend made it public in 2007 and he later resigned.

WHY NOW?

It is unclear why Cook chose this moment to go public, but it comes at critical time in American history when a debate is raging over the legality of gay marriage.

Apple chairman Art Levinson called Cook "courageous."

"(His) decision to speak out will help advance the cause of equality and inclusion far beyond the business world," Levinson was quoted by CNBC as saying.

"On behalf of the board and our entire company, we are incredibly proud to have Tim leading Apple."

Apple has a long history of supporting the LGBT community.

Earlier this year, the company criticised an Arizona bill that would permit businesses to refuse service on religious grounds, a measure that critics said could allow discrimination against gay people.

"...I will personally continue to advocate for equality for all people until my toes point up," Cook said in the article.

"Plenty of colleagues at Apple know I'm gay, and it doesn't seem to make a difference in the way they treat me," he added. - Reuters