One second the building was there, shaken residents of 62nd street said yesterday, but in the next moment it was a cascade of fiery rubble pounding the street.

Authorities said they were investigating whether the four-story building’s collapse at 8:40 a.m. yesterday was the result of a suicide attempt by the owner and sole occupant of the building, Nicholas Bartha, 66, who is reportedly going through a lengthy and bitter divorce. The explosion at 64 E. 62nd St. between Park and Madison avenues was officially caused by an ignited gas leak, the fire commissioner, Nicholas Scoppetta, said.

It wasn’t a quick, loud explosion like a firework, but a deep boom followed by the sound of four stories of stone tumbling to the ground, observers said. Nearby building alarms set off, TV news became static, and phone lines went dead on this upscale block of Manhattan. The power of the blast shattered the windows in the building across the street.

When paramedics arrived, five civilians were discovered with injuries, including one woman who was walking in front of the building just as it came down. Fire department officials said she had numerous cuts and bruises, and was listed in serious but stable condition at the hospital yesterday. Two others had minor injuries and one man treated at the scene refused further medical treatment. Ten firefighters also sustained minor injuries during rescue efforts.

Dr. Bartha, who also practiced medicine out of the basement of the building, survived the collapse and called fire department officials on his cell phone from beneath the rubble. Firefighters subdued part of the fire and removed him from the debris not long after the collapse. He was taken to the hospital in critical condition with severe burns on his face and chest.

With the smell of acrid smoke and smoldering debris strewn across the Upper East Side street it was a sight that reminded many of the Sept. 11 attacks less than five years ago.

“I saw a woman running with blood on her shirt and legs,” a street sweeper who was standing on the corner of Madison and 62nd Street at the time of the explosion, Khalifa Ndiaye, 45, said. “It sounded like a bomb.”

A police source said Dr. Bartha wrote a 15-page “suicide e-mail” to his estranged wife, Cordula Bartha, not long before the explosion. Dr. Bartha allegedly included this line: “You will be transformed from gold digger to ash and rubble digger,” according to an Associated Press article.

Mr. Scoppetta said on NY1’s Inside City Hall last night that the fire department had evidence that this wasn’t the first time Dr. Bartha tried to kill himself with gas in the building.

The city’s Department of Finance said the Neo-Grecian-style townhouse, built in 1881 or 1882 by L.D. Russell and J.B. Wray, is worth more than $6.3 million.The building is part of the Upper East Side Historic District, a spokesman from the Landmarks Department said.The police commissioner, Raymond Kelly, said the department’s Arson and Explosion Squad was investigating the case.

Ms. Bartha, who also uses the last name Hahn, works for the Netherlands consulate as an office manager of the cultural division. Her lawyers, Polly Passonneau and Donna Bennick, said in a joint statement that their client and her family were “deeply saddened and terribly upset” by the events yesterday, but refused to comment on the alleged suicide note.

“The emotional turmoil wrought by the parties’ divorce proceedings, capped by this unspeakable tragedy is difficult enough to bear,” they wrote.

A real estate broker for Prudential Douglas Elliman, Mark Baum, said that Dr. Bartha was considering listing the townhouse in the near future. Mr. Baum, who has worked for Dr. Bartha for six years, said he did not believe that the doctor would blow up the building.

“I don’t like the spin that is going on with him right now,” Mr. Baum said. “He is a super nice guy. I don’t think he would do something like that. He would give you the shirt off his back.”

A rabbi from the nearby Fifth Avenue Synagogue, Yaakov Kermaier, 36, was standing across the street from his wife and children when the building exploded, he said. He screamed for his wife to run with the children, but she yelled back that their 3-week-old son was still inside an apartment with the nanny. The only thing separating them from the explosion, he said, was a single brick wall.

“All I could think was ‘I got to get there as fast as I can,'” he said. “I saw things flying in front of my face.”

He sprinted through the smoke and reached the child and nanny, he said.

Not long before the explosion a number of those who live and work near the building said they could smell gas in the street. At the time of the explosion, a Con Edison mechanic was investigating a report of gas at the Links Club, which abuts Dr. Bartha’s townhouse. The mechanic wasn’t hurt, a spokesman for the company, Joseph Petta, said.

“I could smell gas everywhere,” a maintenance worker for the Links Club, Dahreck Keo, 53, said. “Then I heard a boom,” and dust poured through the basement window, he said.

A spokesman for Con Edison said that it had shut service in Dr. Bartha’s Brownstone last month, responding to a gas leak in the basement. The utilities company said that Dr. Bartha repaired the leak and service was restored after one day.