Wikipedia's impact on the world has yet to peak as the open online encyclopedia aims to double its reach, mainly through expansion in developing countries, founder Jimmy Wales told Reuters.

Wikipedia already has about 400 million users and is in the top 10 most popular websites in the world. It aims to reach a billion through international expansion, starting with India, where it plans its first office outside the United States.

The biggest priority for us is diversifying the contributor base, and we mean that both in English Wikipedia -- we want to diversify the kinds of people who are contributing -- but also geographically, Wales said in an interview with Reuters.

Wikipedia has 17 million articles, more than 3.5 million of them in English, which have been written collaboratively by volunteers around the world. Almost all of its articles can be edited by anyone with access to the site.

I think our real humanitarian impact will be in the next few years as we bring information to people who haven't had it, Wales said, speaking to Reuters at a party in London to celebrate Wikipedia's 10th birthday this week.

He said that along with increasing the number of languages in which Wikipedia articles are published, increasing speed of access was also a priority.

One of the problems we have today is that we are sometimes a little bit slow in India and China. The access times are slow because we don't have enough servers there, he said.

But Wales said he would not compromise on censorship in China, where Wikipedia is accessible but does not have its own servers because it would have to collaborate in filtering its own content.

Access to information, basic information in particular, is a fundamental human right and we won't compromise on it. Of course they don't compromise either, he said.

I meet with the minister there, he meets with me, we've had a lot of conversations, we agree to disagree. We're making progress but it's slow diplomacy.

A year ago, Google announced it may withdraw from China after a serious hacking episode, and said it was no longer willing to self-censor searches. It now has a diminished presence in China.

Wikipedia funds its operations mainly through donations, and has a budget of about $20 million a year.

Canadian journalist and science-fiction writer Cory Doctorow, an advocate of copyright-law liberalization, said the absence of money in Wikipedia's mode of operation was one of its main attractions.

There's one less reason to feel your labor is undervalued, because there's a lot of stuff I would do for free that I wouldn't do for a pittance, he said.

Wales said Wikipedia had no plans to change its non-profit status by selling advertising on the site, which was a place with dialogue and debate that did not come from columnists and bloggers but was aimed at establishing mutual understanding.

That debate is in the form of how do we get it right, how do we explain the world in a mutual way... so in that context we don't want to have a lot of commercialism, he said. It's quite important and we don't see any reason to change it.

(Editing by Paul Casciato)