A Connecticut man whose stepmother allegedly held him captive for 20 years escaped by setting fire to the small room he was held in, officials said.

Authorities responded to the fire and rescued the emaciated 32-year-old man from a 72 sq-foot (6.7 sq metre) room. The alleged captive weighed 68 pounds (30 kilograms) upon his escape and was treated for smoke inhalation.

The man confessed to setting the fire after enduring years of “prolonged abuse, starvation, severe neglect, and inhumane treatment”, police in Waterbury, Connecticut, said.

His stepmother, who is accused of holding him captive and starving him, was charged with kidnapping and cruelty. She has denied the allegations.

When explaining his reasoning for setting the fire, the man told police: “I wanted my freedom.”

Prosecutors allege he was given a sandwich and two small water bottles a day for years. He was only let out of captivity for two hours a day to do chores while under the supervision of his stepmother.

Using hand sanitizer, paper and a lighter he set the fire knowing he could die, a prosecutor said in court on Wednesday.

His stepmother, Kimberly Sullivan, 56, was home at the time of the fire but did not speak to authorities when they arrived on the scene.

Ms Sullivan’s attorney said the accusations were false.

“He was not locked in a room,” the lawyer, Ioannis Kaloidis, told local media. “She did not restrain him in any way. She provided food; she provided shelter. She is blown away by these allegations.”

The fire was set on 17 February, and local police arrested Ms Sullivan on Wednesday.

Waterbury Police Chief Fernando Spagnolo called the details of the case “both heartbreaking and unimaginable”.

Police said the victim told them that he was held captive in his family home in Waterbury from approximately age 11.

“He had been locked in the room for 20 years, and for 20 years he’d been trying to get out of that room,” the prosecutor said.

Authorities were unclear when his father died, but they said his conditions worsened as a result.

When he was found, authorities said he had a body mass index (BMI) of 11. The National Health Service says a healthy range is between 18.5 and 24.9.

Police said that during his captivity, the unnamed man had not received medical or dental care.