Chinese President Xi Jinping has told Prime Minister John Key he is very supportive of Helen Clark's bid for the top job at the UN.

Photo: RNZ / Alexander Robertson

President Xi said China would not use its veto as a permanent member on the UN Security Council against Miss Clark, Mr Key said.

The prime minister said he made a sales pitch for Miss Clark for the secretary-general's job in his official meeting this week with his Chinese counterpart in Beijing.

He said the president spoke warmly of Miss Clark, and recognised she was a good friend of his country, having been prime minister when New Zealand signed the 2008 free trade agreement with China.

Photo: RNZ / Demelza Leslie

"They recognise her as a good friend of China, they recognise the role she had played in the signing of the FTA with China.

"She's been out here quite a bit, they know her well. In the end, the P5 [five permanent members] never say who they are going to vote for, but I would be absolutely stunned if they voted against her."

Miss Clark emerged as one of the front-runners for the top job over the weekend, after UN General Assembly town-hall-style meetings with the candidates.

British bookmaker William Hill now has Miss Clark as the favourite, although the race is set to widen with more nominations expected.

Mr Key, meanwhile, is in Xi'an today as part of his five-day official visit to China, inspecting the region's transportation and logistics hubs.

He will visit the Terracotta Warriors Museum and Great Mosque later tonight.