The first shipments of emergency assistance have begun arriving in storm-wrecked regions of the Philippines, with aid agencies warning the extent of the devastation wreaked by typhoon Haiyan have severely hampered the logistics of bringing vital shelter, water and food to the millions affected.

As David Cameron announced £6m in initial British emergency aid, with the EU promising €3m and the US flying in Marines, aid groups said immediate relief efforts would have to be matched by longer-term planning to assist those who had lost crops, fishing fleets and other infrastructure from the near-200mph winds and 6m storm surge.

They also said that while aid groups had some warning of the typhoon’s approach, efforts to get assistance in place in advance had been hampered by the sheer ferocity of one of the strongest storms ever recorded. “In one town where we had made preparations, even the evacuation centre had to be evacuated, as the storm was so strong,” said Ian Bray from Oxfam.

Among the first aid to arrive was 80 US Marines from their base in Okinawa, southern Japan, flown in to help the Philippines army with logistics. The EU later pledged €3m in aid while Cameron promised £6m, also speaking to his Filipino counterpart, Benigno Aquino, to express his condolences.

One significant challenge is that no one as yet knows the precise extent and location of all the devastation. There has been understandable focus on Tacloban, the main city on Leyte island, with some estimates saying up to 10,000 people could have died here alone. However, there has been little word from other, more remote areas in the path of the storm, both on Leyte and also Samar island, to the north-east, and the northern tip of Cebu, to the west.

Bray said Oxfam already had a team elsewhere on Cebu, who had managed to make their way, with great difficulty, to the north. There, the team estimated, 98% of buildings had been damaged. They saw children holding signs, begging for good and water.

Likening the extent of destruction to the 2004 Indian Ocean tsunami, Bray said: “Getting up there was really difficult, because the roads are strewn with debris and wreckage. Getting to places for immediate response is going to be a big challenge for everyone, because of the level of destruction.”

There was more to think of beyond shelter, clean water and food, he added: “In the immediate aftermath people need these emergency requirements, but in the medium to long term people’s crops will be affected, and things like fishing equipment. Though there’s obviously a massive immediate need there will also be other needs as well, not just today but in the months to come.”

Pete Garratt, disasters emergency manager for the British Red Cross, said access was extremely tricky: “Our team in Tacloban is saying that moving very far out of Tacloban, or even around parts of it, is hard enough. There’s debris, flooding damage and floodwater, and there are some concerns around the looting. People are desperate for supplies. There are some security concerns.”

He said: “It all makes the logistical element of relief supplies very tricky. We had a lot of stuff in Cebu, and more on its way to Cebu from Manila, and international freight coming in to Manila and Cebu. But it’s onwards from Cebu to the most affected areas that’s going to be the really tricky part of this.”