BEIJING — China cremated its only Nobel Peace Prize laureate, Liu Xiaobo, on Saturday, but watchful officials allowed only his widow and a few other mourners to bid farewell to the man who was also the country’s most famous political prisoner.

Later in the day, Mr. Liu’s ashes were lowered into the sea in a simple ceremony, ensuring that there would be no grave on land to serve as a magnet for protests against the Communist Party, especially on the traditional tomb-sweeping day every April.

“As Mozart’s Requiem played, Liu Xiaobo’s wife, Liu Xia, first came forward to stand before his body,” according to an official account of the funeral emailed by the Chinese Ministry of Foreign Affairs. “She gazed upon him for a long time and murmured her final farewells to her husband.”

The mourners bowed three times before Mr. Liu’s body, and Ms. Liu and other family members bowed three times again, the account said. After the cremation, “Ms. Liu received the container of ashes and tightly hugged it to herself,” it said.