WikiLeaks chief Julian Assange has been arrested in London on suspicion of rape after surrendering to a Swedish arrest warrant, setting up a possible extradition fight that could drag on for months.

Assange, 39, was detained after attending a London police station by appointment at 0930 GMT on Tuesday and is due to appear at City of Westminster Magistrates' Court later in the day, the Metropolitan Police said in a statement.

"Officers from the Metropolitan Police Service's Extradition Unit have this morning, Tuesday 7 December, arrested Julian Assange on behalf of the Swedish authorities on suspicion of rape," the statement said.

"He is accused by the Swedish authorities of one count of unlawful coercion, two counts of sexual molestation and one count of rape, all alleged to have been committed in August 2010."

The net has tightened around the Australian former computer hacker since his whistleblower website began releasing thousands of secret US diplomatic cables last week, infuriating Washington and other countries.

Assange's lawyers were not immediately available for comment, but they have said he will fight extradition to Sweden, saying they fear he could then be passed on to the United States from the Scandanavian country.

One of his London-based lawyers, Jennifer Robinson, said he was "isolated and persecuted" and that death threats had been made on blogs against Assange's son.

"I think he will get a fair hearing here in Britain but I think our, his, prospects if he were ever to be returned to the US, which is a real threat, of a fair trial, is, in my view, nigh on impossible," she told the Australian Broadcasting Corp ahead of his arrest.

A court in Stockholm issued an arrest warrant for Assange on November 18.

His lawyers have said the case centres around consensual sex with two women.

Assange could now be embroiled in the extradition process for weeks, or even months.

A spokesman for the Serious Organised Crime Agency (SOCA) told AFP ahead of Assange's arrest that when the subject of a European arrest warrant appears in court they are given the option to consent to their extradition.

If they dispute extradition a further court hearing is set, where the judge hears from prosecutors and from the subject, said the agency, which is responsible for receiving and certifying international arrest warrants.

The judge then decides if extradition should be ordered or the person should be freed.

The individual has seven days to appeal an extradition order. If there is no appeal, the person has to be handed over within the 10 days after the appeal period expires.

Appeals last for as long as the legal process takes, typically months, going up through the appeal court and supreme court if necessary.

Police sources said Assange was unlikely to be granted bail because of the risk he will try to flee the country.

WikiLeaks itself continued to be chased around the globe following its release of thousands of US diplomatic cables, with Swiss authorities shutting down one of Assange's bank accounts on Monday.

WikiLeaks has already been expelled from the United States where politicians have called for Assange to be treated as a terrorist. Supporters of the website have responded by setting up hundreds of "mirror" sites to keep it online.

In one of the latest leaks, US cables released Tuesday showed that NATO had extended an existing defence plan covering Poland to include Estonia, Latvia and Lithuania after they lobbied for extra protection.

Russia said it was "perplexed" by the plans, revealed in the Guardian newspaper, which came just weeks after a NATO-Russia summit hailed as a breakthrough in relations.