MANILA  - The United States, Australia and the United Nations mobilised emergency aid to the Philippines as the scale of the devastation unleashed by Super Typhoon Haiyan emerged Monday.

The Pentagon sent Marines and equipment to assist with the relief effort following the typhoon, which may have killed more than 10,000 people in what is feared to be the country's worst natural disaster.

The United States has sent an additional 180 troops to the Philippines for humanitarian assistance efforts, the Marine Corps said Monday.

Four MV-22B Ospreys - aircraft that can operate in difficult environments - and three KC-130J Hercules planes headed to the disaster zones from Japan over the course of the afternoon and evening, according to a statement.

Even Vietnam, despite coping itself with a mass evacuation programme as a weakened Haiyan swung onto its territory, provided emergency aid worth $100,000 and said it "stands by the Philippine people in this difficult situation".

On the ground, the relief operation was centred on the city of Tacloban on Leyte island, three days after one of the biggest storms in recorded history demolished entire communities across the central Philippines and left countless bodies as well as gnawing desperation in its wake.

Delivering on a promise of quick help from President Barack Obama, about 90 US Marines and sailors based in Japan flew into Tacloban aboard two C-130 Hercules transport aircraft, after receiving a bird's eye view of the immense scale of destruction across Leyte.

They brought communication and logistical equipment to support the Philippine armed forces in their relief operation.

"We are gonna move stuff as they direct, as the Philippine government and the armed forces (ask)," Brigadier General Paul Kennedy, the head of the Okinawa-based 3rd Marine Expedition Brigade, said in Tacloban.

Kennedy's men were the advance guard of a Marine operation that in total will encompass up to nine C-130s plus four MV-22 Ospreys - tilt-rotor planes that can operate without runways - and two P3 Orion aircraft for search and rescue.  "That is what I do, I provide capabilities that are not resident here," Kennedy told reporters.

The Australian government pledged Aus$10 million dollars (US$9.38 million), with Foreign Minister Julie Bishop describing the unfolding tragedy as "absolutely devastating" and on a "massive scale".

The sum includes Aus$4 million towards a UN global appeal and Aus$3 million for Australian non-government organisations. The aid will include tarpaulins, sleeping mats, mosquito nets, water containers and health and hygiene kits.

A team of Australian medics will leave on Wednesday via a C17 military transport plane from Darwin to join disaster experts already on the ground, the government said.

Philippine rescue teams were said to be overwhelmed in their efforts to help those whose homes and livelihoods were destroyed after Haiyan ravaged large swathes of the archipelago Friday.

Officials were struggling to cope with the scale of death and destruction, with reports of violent looters and scarcity of food, drinking water and shelter.

United Nations leader Ban Ki-moon promised UN humanitarian agencies would "respond rapidly to help people in need".

The UN children's fund UNICEF said a cargo plane carrying 60 tonnes of aid including shelters and medicine would arrive in the Philippines Tuesday, to be followed by deliveries of water purification and sanitation equipment.

Pope Francis led 60,000 people in Sunday prayers for the Philippines, urging the faithful to provide "concrete help" to the largely Roman Catholic country.

Other aid mobilised for the Philippines includes:

- The European Commission said it would give three million euros ($4 million) towards the relief efforts.

- Britain offered an emergency support package worth $9.6 million. Germany's embassy in Manila said an initial shipment of 23 tonnes of aid was being flown in and German rescue teams were already at work.

- Japan was Monday sending a disaster relief and medical team of 25 people, while Malaysia also readied a relief crew and cash aid was offered by Taiwan and Singapore.

- New Zealand increased its humanitarian relief on Monday, bringing its total to NZ$2.15 million (US$1.78 million), while Canada has promised up to US$5 million to aid organisations.

- Medecins Sans Frontieres (Doctors Without Borders) said it was sending 200 tonnes of aid including medicine, tents and hygiene kits to arrive mid-week, with the first cargo plane leaving from Dubai on Monday and another from Belgium on Tuesday.

Meanwhile, at least six people died after Typhoon Haiyan slashed across China's south coast and damaged hundreds of homes, state-run media said Monday.

Three pedestrians were hit by falling walls or advertising hoardings in the southern island province of Hainan, a local newspaper said. One drowned in the neighbouring Guangxi Zhuang region, according to the official Xinhua news agency.

Two sailors were found dead after their cargo ship was cast adrift in the storm, Xinhua added, citing maritime rescue authorities in Hainan, and rescuers were still searching for another five crew members lost at sea.