As many have now died from complications as died in the attacks, the Fire Department of New York says.
The Fire Department of New York has said the number of its members who have died from 9/11-related illnesses is now equal to the number lost on the day of the attacks, 343.
Two recent deaths added to the toll.
“With these deaths, we have reached a sombre, remarkable milestone,” New York City Fire Commissioner Laura Kavanagh said in a statement.
“Our hearts break for the families of these members, and all who loved them.”
Soon after the 22nd anniversary of the attacks, emergency medical technician Hilda Vannata died on 20 September from cancer, while retired firefighter Robert Fulco died of pulmonary fibrosis on 23 September, according to city officials.
Both illnesses were a “result of time they spent working in the rescue and recovery at the World Trade Center site,” the New York City Fire Department said in a statement.
Born in Puerto Rico, Vannata, who died at the age of 67, was a mother and served as an emergency services technician for 26 years, according to her obituary.
“She was known by all as a warm and caring person, always going out of her way to help anyone in need,” the obituary said.
Fulco, who died at the age of 73, was born in Brooklyn, New York, according to a memorial page. Well-wishers called him a “true hero”.
Nearly 3,000 people were killed in the 11 September attacks in 2001, with most of the deaths in New York. There, Al-Qaeda militants crashed two US passenger jets they had seized into the twin towers of the World Trade Center. The buildings were set on fire, trapping people on upper floors and enveloping the city in smoke.
The attack marked the largest loss of emergency personnel in US history.
The New York City Fire Department said 11,000 first responders suffer from 11 September-related diseases, including 3,500 with cancer.
“So many of our members showed up for us that fateful day, and so many were lost,” the department said in a statement. “The legacy we create for them is one of honor, and one of promise.”