A helicopter carrying four people crashed into the Yangtze River near Shanghai soon after taking off from an Antarctic expedition ship anchored in the harbor, leaving three injured and the other missing.

"The helicopter flew up only three or four meters - no more than a minute after taking off - when it crashed," said a worker on a nearby ship carrying mud for a tunnel-building project.

The helicopter was hired by the Polar Research Institute of China (PRIC) for the just-concluded 25th expedition to the South Pole on the Snow Dragon. The aircraft was heading home to Feilong Aircraft Company based in Harbin, when the accident happened.

The helicopter fell into the Waigaoqiao area in the Yangtze River about 70 m from the Snow Dragon at 11:20 am.

Three of them, two pilots - Li Baohui and Yang Hua - and technician Tang Lijun were rescued by the mud transportation ship within 20 minutes, but the fourth, a technician named Yang Yongchang was missing as of last night.

The rescued people were treated at No 7 People's Hospital and reported to be in stable condition.

About 13 ships were pressed into service for the search, and by 6:30 pm, a sonar system located the helicopter at the bottom of the river.

The PRIC has leased helicopters from Feilong Company many times for its polar expeditions; and three of the four on the crashed helicopter participated in the latest expedition to the South Pole, including Yang, the missing technician.

The cause of the accident has not been determined.

The Snow Dragon returned to its home harbor in Shanghai on April 8 after its mission to the Antarctic, where China's first inland research station, Kunlun, was built on the highest plateau on the South Pole.