Internet trolls on the site which hosted naked celebrity photos have made what appears to be a threat to film star Emma Watson just hours after she addressed the United Nations on gender equality.

A web page entitled Emma You Are Next, featuring an image of the Harry Potter star next to a countdown, appeared to have been created by a user of image-sharing website 4chan, on which lewd photos of celebrities including actress Jennifer Lawrence and model Kate Upton were posted last month.

It came hours after Emma, 24, a Goodwill Ambassador for UN Women, launched the HeForShe campaign in a speech at the world body in which she appealed to men to speak out for equality.

The web page, which also carries the words "never forget, the biggest to come thus far", sparked debate on social networking sites including Twitter and Tumblr and the timer was set to end at midnight on Friday.

After the first set of hacked images were posted on the internet, Emma said on Twitter: "Even worse than seeing women's privacy violated on social media is reading the accompanying comments that show such a lack of empathy."

And in her UN speech Emma said she wanted to challenge gender stereotypes after she felt she had been "sexualised" in the media at just 14.

She said: "For the record feminism by definition is the belief that men and women should have equal rights and opportunities. It's the theory of the political, economic and social equality of the sexes.

"I started questioning gender-based assumptions a long time ago. When I was eight I was confused about being called bossy because I wanted to direct plays we put on for our parents but the boys were not.

"When I was 14 I started to be sexualised by certain elements of the media. When I was 15 my girl friends started dropping out of their beloved sports teams because they did not want to appear muscly."

Watson added she had been "privileged" when growing up as her parents and teachers had been "inadvertent feminists".

And she said: "Men don't have the benefits of equality either. We don't often talk about men being imprisoned by gender stereotypes - but I can see that they are. And when they are free, things will change for women as a natural consequence.

"If we stop defining each other by what we are not and start defining ourselves by who we are we can all be freer and this is what HeForShe is about. It's about freedom. I want men to take up this mantle."