Google's executive chairman has started a visit to North Korea, which has sparked controversy and fascination.

Eric Schmidt arrived yesterday in a country considered to have the world's most restrictive internet policies. He is part of a delegation that includes former New Mexico governor Bill Richardson.

It is the first trip by an executive from the California-based internet search provider to North Korea.

Also on the delegation is Jared Cohen, director of the Google Ideas think-tank. Mr Cohen is a former State Department policy adviser.

Washington has criticised the trip as not "helpful". North Korea has drawn criticism for launching a long-range rocket last month.

Mr Richardson has called the visit a "private humanitarian mission" but it is not clear what the group hopes to accomplish on the trip.

Mr Schmidt, who arrived on a commercial Air China flight, wants a first-hand look at North Korea's economy and social media during his private visit to the communist nation, his delegation said.

Mr Richardson, speaking ahead of the flight from Beijing, said: "This is not a Google trip, but I'm sure he's interested in some of the economic issues there, the social media aspect. So this is why we are teamed up on this," he said without elaborating on what he meant by the "social media aspect".

He added: "We don't control the visit. They will let us know what the schedule is when we get there."

US officials have criticised the four-day trip.

On December 12 North Korea fired a satellite into space using a long-range rocket. Washington condemned the launch, which it considers a test of ballistic missile technology, as a violation of UN Security Council resolutions barring Pyongyang from developing its nuclear and missile programmes.

The Security Council is deliberating whether to take further action.