Royal Navy aircraft carrier HMS Illustrious has been sent to the Philippines to help with the relief effort following the devastation caused by Typhoon Haiyan.
The vessel, which was taking part in exercises in the Gulf, will arrive in the disaster zone to support the humanitarian operation by November 25, replacing HMS Daring which has already been deployed to the Philippines.
A charity appeal to help the 11.5 million people affected by the disaster has raised £23 million in just two days and the Government has now given more than £20 million in aid.
HMS Illustrious, the Royal Navy's only operational aircraft carrier, has a 900-strong crew and seven helicopters able to provide assistance, as well as the ability to create fresh water, vital in the effort to combat the spread of disease.
Mr Cameron, who announced the deployment of HMS Illustrious during a visit to India, said: "What happened in the Philippines is an absolute tragedy. You can see the devastation, the suffering, and it's quite clear that we are going to need long-term help for those people.
"As ever, the British people have been very generous with their donations.
"The British Government has already pledged over £20 million, which makes us one of the most generous donors anywhere in the world.
"But it's practical action that's needed as well. That's why I sent HMS Daring to go and help in the Philippines and I can announce today that once Daring has started its work, we are actually going to be able to replace in time HMS Daring with HMS Illustrious, which is, of course, a carrier with helicopters - seven times as many helicopters as on HMS Daring and with the key ability to process fresh water, so we will be giving further assistance in the best way we can."
A civilian Antonov cargo aircraft and at least one RAF C-17 transport plane have also been assigned to the relief effort.
International Development Secretary Justine Greening said: "HMS Illustrious will bring extra air support which can help unblock transport bottlenecks. In addition, the UK will send specialist aircraft loaded with heavy-duty equipment to speed up the offloading of relief supplies at airfields.
"We are now in peak danger period for the spread of infectious disease, so HMS Illustrious' capability to provide drinking water will be invaluable.
"The UK has now given more than £20 million in aid. Not only are we helping thousands of people in desperate need but British equipment and personnel will help clear the roads so international humanitarian relief can get to where it needs to go."
News about the latest military support came as the Disasters Emergency Committee (DEC) announced that its Philippines typhoon appeal has raised more than £23 million in just two days.
The funds, made up of online, text and phone donations, will be used to deliver food, water, household items and tarpaulin for shelter to people who have had their homes damaged or destroyed and are in desperate need of food, water and shelter.
Saleh Saeed, DEC chief executive, said: "The public's reaction to the sheer devastation that has been left by Typhoon Haiyan is quite simply remarkable. We are so grateful for the huge amount of donations which are vital to fund the work done by our emergency teams.
"This has already become one of our most generously supported appeals but there is still a huge humanitarian need for help. Our priority is to provide food, water and shelter to those affected. Money raised will go directly to delivering these essentials and it's important we continue to provide this support."
Authorities in the Philippines said 2,357 people have been confirmed dead in the disaster, but that figure is expected to rise, perhaps significantly, when information is collected from other areas.
Workers in Tacloban, one of the cities hardest hit by the typhoon, have been burying scores of unidentified bodies in a hillside mass burial as desperately needed aid began to reach some of the half-million people displaced by the disaster.
Baroness Amos, the UN humanitarian chief, said some 11.5 million people have been affected by the typhoon, which includes people who lost their loved ones, were injured, and suffered damage to their homes, business or livelihoods.
"The situation is dismal ... tens of thousands of people are living in the open ... exposed to rain and wind," she told reporters in the Philippines' capital Manila.
She said the immediate priority for humanitarian agencies over the next few days is to transport and distribute high-energy biscuits and other food, tarpaulins, tents, clean drinking water and basic sanitation services.
"I think we are all extremely distressed that this is day six and we have not managed to reach everyone," she said.
Captain Mike Utley, the commanding officer of HMS Illustrious, said: "We are very well configured and trained to render the kind of assistance we believe is needed in the Philippines in support of the international aid effort.
"The young sailors and airmen in my crew have seen the news reports coming in from the Philippines and no one is in any doubt of the scale of the task ahead of us, but all want to help in whatever way they can. I am very proud indeed of the way they have reacted to this."
He continued: "We are used to operating with embedded teams from the army and the RAF. In addition, we have repeatedly proven our ability to inter-operate with other nations including the United States and civilian aid organisations with whom we expect to see a lot of interaction. As always, we will be ready for anything."
The United States already has a considerable naval presence in the area, with the USS George Washington aircraft carrier setting up a position off the coast of Samar Island to assess the damage and provide medical and water supplies.
The carrier and its strike group took 21 helicopters to the area, which can help reach the most inaccessible areas.
In addition to the USS George Washington, about half a dozen other US ships - including a destroyer and two huge supply vessels - are already in the area, along with two P-3 aircraft being used to survey the damage from the sky.
Sebastian Rhodes Stampa, from the United Nations Office for the Coordination of Humanitarian Affairs, said the effects of disease outbreaks in the typhoon-shattered towns and cities could be "very large".
He told Channel 4 News the humanitarian response was "slower than we would have liked" and it was important to co-ordinate the relief effort.
He added: "The secondary order of effect may be very large. We have that first order of effect which is the disaster itself and then very shortly thereafter we must be incredibly conscious there may be the second order of effect - it could be waterborne disease, it could be cholera, it could be leptospirosis.
"We have disease surveillance out, we are trying to bolster that at the moment with the department for health."