energy biscuits and tons of emergency medical aid were heading to Haiti Wednesday as governments and aid groups launched a massive relief effort for the estimated 3 million people reeling from a devastating earthquake. Aid officials in the impoverished Caribbean nation worked to clear rubble from roads, build makeshift hospitals and remove bodies from the rubble despite transportation problems and broken phone lines. Wintry weather in Europe added to the challenge, with snow temporarily delaying a British aid flight with 64 firefighters and rescue dogs at Gatwick airport. As it struggled to gauge the full scale of the catastrophe, the United Nations said it was rushing food, personnel and medical supplies to alleviate the “major humanitarian emergency.” It also confirmed at least 140 members of its own staff were missing under flattened roofs in the Haitian capital, Port-au-Prince. “We'll be using whatever roads are passable to get aid to Port-au-Prince, and if possible we'll bring helicopters in,” said Emilia Casella, a spokeswoman for the UN food agency. Its 200 staff in Haiti were trying to deliver high-energy biscuits and other supplies, despite looting and the threat of violence in a nation long plagued by lawlessness. But the sheer number of dead bodies was expected to pose a problem. The World Health Organization said it has sent specialists to help clear the city of corpses and prevent the spread of disease, and the Red Cross was sending a plane Thursday loaded mainly with body bags. The Red Cross estimated that 3 million people will require aid, ranging from shelter to food and clean water, and said many Haitians could need relief for a full year. “There are many, many people trapped in the rubble,” said Paul Conneally, spokesman for the International Federation of Red Cross and Red Crescent societies. “We're not optimistic at the moment.” US Secretary of State Hillary Rodham Clinton said the US was offering full assistance - civilian and military. Ships, helicopters, transport planes and a 2,000-member Marine unit are either on the way or likely to begin moving soon, US officials said. France dispatched 65 rubble-clearing specialists and six sniffer dogs for Haiti, while Spain was rushing three airplanes of rescuers and 100 tons of tents, blankets and cooking kits. Israel was sending in an elite army rescue unit of engineers and doctors. A military reconnaissance team from Canada was arriving in Haiti on Wednesday aboard a C-130 transport plane to assess the need for donated mosquito nets, basic household goods, tents and sanitation packages. Dozens of other countries, including Britain, Germany, China, Mexico, Iceland and Venezuela, pledged rescue teams, doctors, cash and supplies.