Rudy Giuliani, the former New York City mayor and long-time champion of President Donald Trump, is recovering from pneumonia and "is now breathing on his own", according to his spokesman.

In a statement on X, spokesman Ted Goodman said that Giuliani has had "restrictive airway disease" since the 9/11 terror attacks that diminished his ability to fight off pneumonia.

"The virus quickly overwhelmed his body, requiring mechanical ventilation to maintain adequate oxygen and stabilize his condition," Goodman said. But he added that Giuliani, "the ultimate fighter", is now "winning this battle".

Giuliani, 81, remains in hospital, "in critical but stable condition," Goodman said.

"On September 11th, Mayor Giuliani ran toward the towers to help those in need, which later led to a diagnosis of restrictive airway disease," Goodman said.

After "mechanical ventilation," Goodman said Giuliani "is now breathing on his own, with his family and primary medical provider at his side."

Diseases caused by the toxic dust and smoke in the 9/11 attacks have continued to cause health issues among victims and first responders, including firefighters, police officers and medical workers.

These diseases have claimed twice as many lives in the 25 years since as the attacks themselves, researchers say.

His spokesman announced on Sunday that Giuliani had been taken to hospital and was in critical condition but did not provide details about his illness.

Giuliani earned the nickname "America's Mayor" after leading New York City through the aftermath of the 9/11 attacks.

In recognition of his leadership, he was awarded an honorary knighthood (KBE) by Queen Elizabeth in 2002.

His second term in office ended at the end of 2001 and he later made an unsuccessful presidential run for the Republican Party nomination.

He was a key backer of Trump's 2016 White House run, most publicly at the Republican National Convention. He later became Trump's personal lawyer.

After the 2020 presidential election, Giuliani and other advisers travelled across the country making false claims about the results, accusing Trump's opponent Joe Biden of attempting to steal the election.

Later, a jury forced him to pay two election workers he had accused of ballot fraud $148m (£108m) for defamation. He was later disbarred – meaning his legal credentials were stripped – due to his false claims about the election. He also declared bankruptcy.

In his social media post expressing concern for Giuliani's health, Trump repeated his false claims about Democrats stealing the 2020 election, and said the ex-mayor had been "treated so badly" by Democrats.

"They cheated on the Elections, fabricated hundreds of stories, did anything possible to destroy our Nation, and now, look at Rudy. So sad!" he said.

Last September, Giuliani was a passenger in a Ford Bronco when it was struck from behind in the US state of New Hampshire.

He suffered a fractured thoracic vertebrae, multiple lacerations and contusions, and injuries to his left arm and lower leg, his security guard said at the time.