9/11 anniversary: Biden, Bush and Harris urge unity as US marks 20 years since attacks – as it happened

Biden and Harris among leaders at ceremonies in New York, at the Pentagon and in Shanksville, Pennsylvania

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10.37pm BST

Our coverage of the 20th anniversary of the 9/11 attacks is coming to a close. Thank you for reading. Here is some of our coverage:

9.50pm BST

Twenty years after Lower Manhattan was covered in toxic dust from the World Trade Center, health problems persist for survivors and first responders at the Twin Towers, and for residents who lived nearby.

According to the Associated Press, 111,000 people are part of the World Trade Center Health Program, which provides free medical care to persons with health problems possibly tied to the dust.

To date, the U.S. has spent $11.7 billion on care and compensation for those exposed to the dust -- about $4.6 billion more than it gave to the families of people killed or injured on Sept. 11, 2001. More than 40,000 people have gotten payments from a government fund for people with illnesses potentially linked to the attacks.

Scientists still can't say for certain how many people developed health problems as a result of exposure to the tons of pulverized concrete, glass, asbestos, gypsum and God knows what else that fell on Lower Manhattan when the towers fell.

The largest number of people enrolled in the federal health program suffer from chronic inflammation of their sinus or nasal cavities or from reflux disease, a condition that can cause symptoms including heartburn, sore throat and a chronic cough.

The reasons for this are not well understood. Doctors say it could be related to their bodies getting stuck in cycles of chronic inflammation initially triggered by irritation from the dust.

Post-traumatic stress disorder has emerged as one of the most common, persistent health conditions, afflicting about 12,500 people enrolled in the health program. Nearly 19,000 enrollees have a mental health problem believed to be linked to the attacks. More than 4,000 patients have some type of chronic obstructive pulmonary disease, a family of potentially debilitating breathing problems.

Time has helped heal some physical ailments, but not others. Many first responders who developed a chronic cough later had it fade, or disappear entirely, but others have shown little improvement.