The bulk carrier was captured in mid-October, northeast of the Seychelles as it was sailing from South Africa to India.
It was carrying about 76,000 tonnes of coal.
The De Xin Hai was the first Chinese vessel to be hijacked since China deployed a three-ship squadron to the Gulf of Aden last year, joining Britain, India, Iran, the US, France and other countries in anti-piracy patrols.
A purported pirate, who identified himself as Hassan, told the Reuters news agency on Sunday that the crew and the vessel would be released in the coming days after the ransom had been paid.
"A helicopter dropped the ransom money on to the ship. We have received $4 million," he said.
"We hope to disembark in a few hours.
"The crew is safe and, although they will not have their freedom for a few more days, they are all happy now."
Heavily armed gangs from Somalia have made tens of millions of dollars hijacking vessels in the Indian Ocean and the strategic Gulf of Aden.
The hijacking has highlighted China's growing presence on global shipping
lanes, and brought warnings that Beijing could use military force against the pirates.
Pirate attacks in the area nearly doubled in 2009 over a year earlier, despite the deployment in December 2008 of the European Union Naval Force, the first international force specifically to counter Somali pirates.
Somali pirates currently hold at least 10 vessels and more than 200 crew members for ransom.