By Manuel Mogato

MANILA, Nov 19 (Reuters) - The Philippines will divide up the typhoon-ravaged central Visayas between countries to maximise relief efforts, a senior officer said, as President Benigno Aquino won guarded praise for improving aid distribution 11 days after the storm hit.

But the country is still struggling to get aid to devastated areas due to the extent of the destruction, which has left four million people displaced, threatening Aquino's reforms that have helped transform the Philippines into one of Asia's fastest-growing and hottest emerging economies.

Aquino is now personally overseeing relief operations in the worst-hit city of Tacloban in one of Asia's biggest humanitarian efforts which could last months, if not years.

The military commander of the Visayas, Lieutenant-General Roy Deveraturda, said the relief plan was to now cut the region into blocks and decide which military forces operate where.

"We're planning to ask the British Royal Navy to concentrate on the western Visayas region to assess and deliver food, water and supplies to smaller islands... We already have the Americans in Samar and Leyte and Israeli doctors and relief teams in northern tip of Cebu," he said.

About 50 U.S. ships and aircraft have been mobilized in the disaster zone, led by the USS George Washington aircraft carrier. The USS Freedom, a combat ship for coastal waters, arrived in Brunei on Monday en route to the Philippines.

Authorities estimate more than 3,900 people were killed when Typhoon Haiyan made landfall on Nov. 8 and the sea surged ashore. Estimates of the death toll have varied widely, and the governor of worst-hit Leyte province said more than 4,000 people could have been killed on the island of Leyte alone.

The International Labour Organization said five million workers had had their lives turned upside down.

"But this is not just a matter of numbers," ILO Philippine Office director Lawrence Jeff Johnson said. "These are people whose livelihoods have been destroyed."

The United Nations has expressed fear that some islands may still not have been reached by aid workers, but the government denied this.

"Basically, we've provided everyone with relief. What we are doing right now is sustainment," said Eduardo del Rosario, director of the National Disaster Risk Reduction and Management Council.

NO LONG-TERM THREAT TO ECONOMY

A British destroyer anchored off Cebu and its helicopters were flying mercy missions to smaller islands, Deveraturda said. Once a larger British carrier arrived with seven helicopters, that would be the best platform for relief for the western Visayas. A Canadian team with a C10 plane has been operating in and around the western island of Iloilo.