From deformed infants to grandparents with cancer, families near Vietnam's Danang Airbase have long blamed the toxic legacy of war for their ills. Now after a decades-long wait, a historic "Agent Orange" clean-up is finally beginning.

The base was a key site in the US defoliant program during the Vietnam War, and much of the 80 million litres (21 million gallons) of Agent Orange used during "Operation Ranch Hand" was mixed, stored and loaded onto planes there.

On Thursday, the US and Vietnam began a long-awaited joint cleanup effort at the site -- using technology which will heat the contaminated soil to temperatures high enough to break dioxin down into harmless compounds.

The defoliants were sprayed over vast swathes of jungle in South Vietnam in an attempt to flush out Viet Cong communist guerrillas by depriving them of tree cover and food.

"During the war, when we lived right by the runway, some nights we would have to cover our mouths because of a strange smell," Danang resident Nguyen Thi Binh, 78, told AFP.

Three of Binh's five children are severely mentally and physically disabled. For years she thought this was due to sins committed in a past life, but now believes it could be due to her and her late husband's dioxin exposure.

"I heard it might be Agent Orange," she told AFP in her tiny house in Danang city as her adult daughters crawled around her like infants.

Washington still disputes the "uncertain" link between dioxin exposure and ill health.

Nonetheless speaking at the launch ceremony for the decontamination operation, US Ambassador David Shear described it as a "historic milestone".

"We're cleaning up this mess," he said, adding the US would in future undertake an environmental assessment of another hotspot, the Bien Hoa airbase.

"We're also committed to people in Vietnam with disabilities, regardless of cause," he added.

The $43 million project comes as the former foes draw closer in the face of rising Chinese assertiveness in the South China Sea.

The Danang Airbase is one of three "dioxin hotspots" -- alongside Bien Hoa and Phu Cat airbases -- where concentrations of extremely toxic contaminants from Agent Orange are nearly 400 times the globally accepted maximum standard.

Until five years ago, when the area was finally sealed off, Danang residents such as Binh fished, bathed and harvested lotus plants from the Sen Lake -- and ate local fish with more than three times the safe level of dioxin.

As a result, victims groups say, rates of cancer, birth deformities and other dioxin-related diseases are higher than the national average in the area -- and the health threat lingers.

"In hotspots like Danang Airbase we are still finding very young people who are affected by (Agent Orange related) diseases," said Nguyen Van Rinh, chairman of the Vietnam Association for Victims of Agent Orange/Dioxin (VAVA).

"The government doesn't have the capacity to move them out of contaminated areas," the 71-year-old retired general told AFP.

Hanoi says up to three million Vietnamese people were exposed to Agent Orange, and that one million suffer grave health repercussions today, including at least 150,000 children born with birth defects.

"There remain serious consequence from Agent Orange," Vietnam's Deputy Minister of Defence Nguyen Chi Vinh said at the Thursday ceremony.

An attempt by Vietnamese victims to obtain compensation from the United States had little success, and the US Supreme Court in 2009 declined to take up the case.

American veterans have received billions of dollars for diseases linked to Agent Orange but neither the US government nor the chemical manufacturers ever admitted liability.

In Vietnam, the link between exposure and diseases is "uncertain", US Embassy spokesman Christopher Hodges told AFP.

Since 1989 Washington has given $54 million to help Vietnamese with disabilities "regardless of cause," and some $20 million has been set aside for the Danang clean-up and disability projects in 2012, he said.

For the victims, the decontamination project is long overdue.

"I think that this clean-up is too late because so many people have already been affected" by dioxin, said Nguyen Thi Hien, who heads VAVA in Danang.

The eventual price tag for cleaning all the country's hotspots and supporting victims could run to $450 million, according to some estimates.

Nguyen Thi Luu, 38, has lived by the Danang Airbase for 13 years. Her daughter, now 11, was born severely mentally disabled with disfiguring facial deformities.

"The doctors told me she was just born like this," she told AFP. "I don't understand. With a child like this, life is very hard."