An aircraft believed to be carrying Edward Snowden landed in Moscow on Sunday after Hong Kong let the former US security contractor leave the territory, despite Washington's efforts to extradite him to face espionage charges.

The anti-secrecy group WikiLeaks said Snowden was heading for a "democratic nation" which it did not name, although a source at the Russian airline Aeroflot said he would fly on within 24 hours to Cuba and then planned to go to Venezuela.

The Hong Kong government said earlier it had "no legal basis" to prevent Snowden leaving because the US government had failed to provide enough information to justify its provisional arrest warrant for him.

Snowden, 30, landed at Sheremetyevo Airport in the north of Moscow at 5:05 pm, but there was no immediate official confirmation of where he would head next, an AFP correspondent at the airport said.

Snowden, who worked for the National Security Agency, had been hiding in Hong Kong since leaking details about US surveillance activities to news media.

"It's a shocker," said Simon Young, a law professor with Hong Kong University. "I thought he was going to stay and fight it out. The US government will be irate."

A source at Aeroflot said Snowden would fly from Moscow to Cuba on Monday and then planned to go on to Venezuela. The South China Morning Post earlier said his final destination might be Ecuador or Iceland.