Prince Charles is being accused of hypocrisy after planning to fly more than 11,000 kilometres with a staff of 20 people on a jumbo jet to accept an environmental award.

Charles, who has spoken publicly on the threat of climate change, will receive a Global Environmental Citizen prize from Harvard Medical School's Centre for Health and the Global Environment later this month.

Former American vice-president Al Gore, who recently made a documentary about climate change, will present the award at a glitzy ceremony attended by actress Meryl Streep.

Environmentalists say he could accept the award via video link, but the prince's office said he is making the two-day visit to Philadelphia and New York at the request of the Foreign Office to promote climate change as a key priority of the British government.

A spokesperson for the environmental group Plane Stupid accused Prince Charles of "green hypocrisy."

"Flying to an environmental award ceremony is a bit like turning up to an Oxfam award ceremony in a stretch limo," said Joss Garman.

A representative of Britain's Green party said he was "disappointed" in the prince.

"I am disappointed to see that — much like Tony Blair — his recognition of the threat posed by climate change does not extend to toning down his personal flying habits. Why can't he set a genuine example and accept the award by video link instead?" said Sian Berry.

Charles and his wife Camilla will be in the U.S. Jan. 27-28.