BEIJING — A blind Chinese legal activist was hurriedly taken from a hospital and put on a plane for the United States on Saturday, closing a nearly monthlong diplomatic tussle that had tested U.S.-China relations.

Chen Guangcheng, sitting in a wheelchair and accompanied by his wife and two children, boarded United Airlines Flight 88 for the 12-hour flight to Newark, outside New York City, a few hours after Chinese authorities suddenly told him to pack and prepare to leave.

“Thousands of thoughts are surging to my mind,” Chen said at the airport. His concerns, he said, included whether authorities would retaliate for his negotiated departure by punishing his relatives left behind. It also is unclear whether the government will allow him to return.

A self-taught legal activist, Chen asked his supporters and others in the activist community for their understanding of his desire to leave the front lines of the rights struggle in China.

“I am requesting a leave of absence, and I hope that they will understand,” he said.

The Chens’ departure to the United States marks the conclusion of nearly a month of uncertainty and years of mistreatment by local authorities for the activist.