WikiLeaks founder Julian Assange was holed up in the Ecuadorian embassy in London on Wednesday after making a dramatic bid to avoid extradition to Sweden over alleged sex crimes.

The 40-year-old, who last week exhausted all his legal options in Britain, walked into the embassy Tuesday and applied for political asylum, as time ran out in his marathon legal battle to avoid being sent to Sweden.

Quito was examining the request after the latest surprise twist in a case dating back to December 2010, when the Australian former computer hacker was first detained in London on a European arrest warrant issued by Sweden.

Britain's Foreign Office said Assange was now "beyond the reach of the police" as he was on diplomatic territory, but stressed it would seek to work with the Ecuadorian authorities "to resolve this situation as soon as possible".

A police officer entered the embassy and left again after a short time overnight Tuesday.

Early Wednesday, around 30 reporters and photographers, and a handful of police officers, were outside the embassy, situated in the upmarket London district of Knightsbridge, near the well-known Harrods department store.

Assange will remain at the embassy under the protection of the Ecuadorian government while his application is considered.

The white-haired Australian confirmed in a statement he was seeking "diplomatic sanctuary and political asylum" and expressed his gratitude to the Ecuadorian government for considering his request.

The embassy said in a statement: "The decision to consider Mr Assange's application for protective asylum should in no way be interpreted as the government of Ecuador interfering in the judicial processes of either the United Kingdom or Sweden."

It confirmed it would be seeking the views of London, Stockholm and Washington to make sure it complied with international law.

In the Ecuadorian capital Quito, Foreign Minister Ricardo Patino confirmed his government was "examining the request" from Assange.

The request for asylum came after the Supreme Court last week rejected an application by Assange to reopen his appeal against extradition.

The decision closed Assange's last legal avenue, although he could still take his case to the European Court of Human Rights.

He maintains that the moves to extradite him to Sweden for questioning over allegations of rape and sexual assault are politically motivated and the real aim is for him to be handed over to US authorities.

WikiLeaks enraged Washington by releasing a flood of classified US information about the wars in Iraq and Afghanistan.

It also published more than 250,000 classified US diplomatic cables, revealing often candid assessments of a huge range of issues as well as the views of other governments.

Assange's mother Christine said her son's decision to turn to Ecuador was a "last desperate effort" and expressed hope that it or "another third-world country" would grant him sanctuary.

"No doubt the Americans are intimidating Ecuador right now to try and back off," she told reporters.

"I thought, 'good on you, mate'.

"I hope the third world can stand up for what's morally right when the first world can't and won't because they've got their snouts in the trough, rolling over for US greed and big business."

Prime Minister Julia Gillard said Australia would continue to offer consular assistance to Assange "just as we do support any Australian overseas who faces legal difficulties or dilemmas".

Ecuador offered Assange residency in 2010, with the government saying at the time it wanted to invite Assange to speak in Ecuador after expressing concern about some of the alleged US activities revealed by WikiLeaks.

Assange interviewed Ecuador's President Rafael Correa for his talk show aired by Russia's RT TV station in April.

He is on £200,000 ($315,000, 250,000 euros) bail, put up by celebrity supporters including filmmaker Ken Loach and Jemima Khan, the former wife of Pakistan cricket captain turned politician Imran Khan.

Helena Kennedy, a human rights lawyer who has advised Assange's legal team, told BBC radio that the next steps might include negotiations with Sweden to secure an undertaking that he would not be sent to the United States.

If that is received, "I imagine the Ecuadorians will be happy to let him proceed to Sweden," she told BBC radio.

Assange's lawyers have until June 28 to apply to the European court to consider his case on the basis that he has not had a fair hearing from the British courts. (AFP)