Chen Guangcheng, the Chinese human rights activist who ignited a diplomatic frenzy when he escaped house arrest last month, is believed to have left Beijing airport Saturday on a flight bound for New York.
He and his family are thought to have boarded a United flight from Beijing to Newark International Airport.
The plane took off nearly two hours later than scheduled from Beijing.
When he reaches the United States, Chen is due to begin a new chapter in his life as a student at New York University.
China has said that Chen, who is blind, can apply to study abroad.
Chen said Wednesday he had received passport applications for himself and his family.
U.S. authorities have completed all the processing for Chen, his wife and two children to travel to the United States, where Chen has been invited to study by NYU, State Department spokeswoman Victoria Nuland said this week.
"He is continuing to work with his government," she said. "Our information is that those conversations, contacts, and processing continue."
Earlier this week, U.S. lawmakers listened to Chen describing reprisals that he said his relatives continue to suffer at the hands of the authorities in Shandong Province in eastern China.
"My elder brother was taken away by these thugs without any reasoning and then they came back and started beating up my nephew, and they used stakes and violently beat him up," Chen told the House Foreign Affairs Committee in a telephone call from his hospital room.
Chen added that his relatives' homes had been broken into and they had been beaten by people working for the government.
Chen said his nephew Chen Kegui tried to defend himself and now faces a "totally trumped-up" charge of attempted homicide.
"After my nephew was beaten up, he actually was waiting to surrender himself and the police come back again and violently beat up my sister-in-law," Chen said.
The authorities in Linyi, the city that oversees Chen's village, had issued a statement accusing Chen Kegui of injuring government officials with a knife and saying he would be dealt with according to the law. They have declined to comment on the matter since.
ChinaAid urged the international community to continue to monitor the situation for Chen's extended family in China, amid concerns over possible reprisals by the authorities.
After spending six days in the U.S. Embassy following his escape from house arrest, the prominent human rights activist left for a hospital, but then pleaded to be allowed to leave China. His spell in the U.S. Embassy caused a diplomatic firestorm, coming as U.S. Secretary of State Hillary Clinton was about to visit China.
Chen was sentenced in 2006 to four years and three months in prison for "damaging property and organizing a mob to disturb traffic" -- charges that his supporters maintain were trumped up by the authorities to punish his legal advocacy for victims of what he called abusive family-planning policies, including forced abortions and sterilization.