BEIJING -- China plans to conduct several manned space flights from 2019 to 2022, during which a 60-tonne space station will be assembled and built, said Wang Zhaoyao, director of China's manned space program office, Friday.

"Tianzhou-1, China's first cargo spacecraft, was the last flight mission of the country's manned space program before the construction of a permanent space station," Wang said at a press conference.

The spacecraft and Tiangong-2 space lab completed their first in-orbit refueling late Thursday, marking the completion of the country's space lab mission.

"The successful conclusion of the mission shows that China's manned space program has entered the space station era," Wang said.

"The space station program has been progressing steadily with its key technologies and plans already completed and its relevant flight products being tested," he said. "Chinese astronauts are preparing for the space station era. They are expected to stay in space for three to six months or even longer during future missions."

Two astronauts, Jing Haipeng and Chen Dong, completed their 33-day journey, the longest mission in the country's manned space program to date, onboard the Shenzhou-11 spacecraft on Nov 18 last year.

Wang said the astronauts would be engaged in more extra-vehicular activities during the construction of the space station, which could pose challenges.