The pirates attacked the ship early Friday in the Gulf of Oman near the Iranian port of Chabahar, said the official Xinhua news agency, citing China's embassy in Tehran.
"Nine Somali pirates climbed onto the cargo ship" using ladders, opened fire and seized the crew members, said the agency.
China's ambassador in Tehran, Yu Hongyang, demanded swift action from Iran, which dispatched its navy to rescue the crew.
Two warships caught up with the ship, the Panama-registered Xianghuamen, which belongs to company in eastern China, and the pirates "threw their weapons into the sea and surrendered to the Iranian navy," Xinhua said.
Following the hijacking, Hongyang had urged Tehran to make the safety of the crew its "first priority", adding that the Chinese government and foreign ministry had expressed concern about the incident.
The freighter, which had set off from Singapore and was heading to a port in southwestern Iran, had its engine damaged in the attack and is being repaired, Xinhua said.
The waters of the Arabian Sea, at the northern tip of the Indian Ocean, have seen hundreds of pirate attacks in recent years, with Chinese shipping vessels routinely targeted.
China has also been heavily involved in anti-piracy missions in the Gulf of Aden, off the coast of Somalia, and in international waters near the Gulf of Oman.
About 85 percent of China's oil imports are routed via the Gulf of Aden and through the Indian Ocean, making the region extremely important for Chinese trade.
Since 2008, China has sent 10 escort missions and more than 8,000 military personnel to the Gulf of Aden, escorting more than 4,300 vessels in the process, state-run China Daily said last year.
In June last year, a Chinese shipping vessel and a crew of 29 were released by pirates after being held captive for 207 days.
China has also formed military links in Africa and in the Indian Ocean in order to protect its growing economic interests in the region, including its ocean-going transport ships.
In December last year, Beijing not only committed to support Ugandan forces operating in Somalia but also pledged to help the Seychelles fight piracy.
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China and Iran have been enjoying cordial relationship for centuries and both know they can count on each other. The two countries have very few friends among member states of the international community, So they look out for each other and hold their own in crisis.
Pakistan,iran & china should be together then no one can give them any threats...
Is this the picture of freighter carrying tens of thousands of Iron ore? No! You guys are pathetic.
Chinese government demanded or requested Iranian navy? I think there is a big difference in two words.