The United Nations health agency has appealed for $28 million to fund a six-month action plan to help survivors of this month's catastrophic cyclone in Myanmar.

The plan is designed for the areas most affected by Cyclone Nargis earlier this month - the Ayeyarwady Delta region and the country's biggest city, Yangon- with a particular focus on people living in temporary shelters and relocations, the World Health Organization (WHO) said in a press statement.

U.N. humanitarian agencies estimate that more than 77,000 people have died and 55,000 others are missing since Cyclone Nargis struck on 2 May. As many as 500,000 to 600,000 people, mainly in the delta, have had to be relocated.

The fund raised for the action plan will be used in part to strengthen surveillance against potential outbreaks of infections diseases, immunize locals for measles and polio, and provide extra emergency medicines, equipment and insecticide-treated bed nets, the WHO said.

The cyclone destroyed about half of the health-care system in the delta and Yangon of Myanmar, also known as Burma.