UNITED NATIONS, Nov. 12 (Xinhua) -- As the magnitude of the devastation wrought by Typhoon Haiyan unfolds in the Philippines, the United Nations and its partners are mounting a massive humanitarian operation, battling heavy rains, blocked roads and damaged airstrips and seaports to reach millions across the region desperate for food, water and other basic necessities.

Valerie Amos, UN under-secretary-general for humanitarian affairs, launched a 300-million-U.S. dollar emergency appeal from the Philippines capital, Manila, earlier Tuesday.

Meanwhile, UN and other relief agencies report that transport logistics remains the biggest challenge due to the widespread damage to infrastructure and the large amount of debris blocking airports, roads and other access routes. Electric lines have been cut and, in some places, heavy ships have been thrown inland.

The UN World Food Program (WFP) said wrecked infrastructure is making humanitarian efforts a "logistics nightmare." The agency has asked for 83 million U.S. dollars for logistics, food and emergency telecommunications equipment.

Forty-four metric tons of High Energy Biscuits (HEBs) are due to arrive in the country Tuesday from the UN Humanitarian Response Depot (UNHRD) in Dubai, with additional biscuits and rice being mobilized from the region.

Also on Tuesday, the UN Children's Fund (UNICEF) said that it is appealing for 34 million U.S. dollars to aid the four million children of the Philippines who survived Typhoon Haiyan. The appeal is a first estimate of the requirements needed to help children and their families recover, and is expected to cover 6 months. It is especially pressing because many of the regions slammed by Typhoon Haiyan are reportedly without electricity, clean water, food and medicine.

Typhoon Haiyan, among the most powerful in history, slammed into the eastern Philippine city of Tacloban on Friday and cut a path of devastation barreling west across the archipelago nation. More than 11 million people have been affected by what the UN World Meteorological Organization (WMO) has called the strongest tropical cyclone so far this year and one of the most intense on record.