China has pledged to make an "all out" effort to rescue a cargo ship with 25 crew on board that has been hijacked by pirates in the Indian Ocean.

The De Xin Hai was seized early on Monday about 1,100km (700 miles) east of the Somali coast.

An associate of the pirates has reportedly warned that a rescue attempt would put the crew's lives at risk.

The EU's anti-piracy naval mission said the ship was being tracked and the crew appeared to be in good condition.

The hijacking is believed to be the first time a ship has been seized between the Seychelles and Maldives, in a sign that pirates have expanded the reach of their operations.

The De Xin Hai, owned by the Qingdao Ocean Shipping Company, was transporting coal from South Africa to India.

Pirate warning

In Beijing, foreign ministry spokesman Ma Zhaoxu said China would make "all-out efforts to rescue the hijacked ship and personnel".

He said China had "actively started rescue operations" for the ship, without giving details.

Other Chinese ships have been ordered to stay away from the area "in case of accident or danger," Mr Ma said.

China sent three warships to the region late last year to help guard against pirate attacks.

An associate of the pirates who seized the ship told Reuters news agency that China should not "endanger the lives of their people with a rescue operation".

"If they try that we will execute the whole crew," said the associate, Hassan, from the pirate stronghold of Haradheere in Somalia.

"We tell them to change their mind regarding any rescue, otherwise they will regret it. We know what they are planning to do."

John Harbour, a spokesman for the EU Navfor Maritime Patrol, said one of its aircraft had located the vessel after Monday's attack.

"The aircraft spotted at least four pirates on the deck and the vessel is towing two skiffs. It was last reported heading west towards the Somali coast," he said.

Hassan told Reuters that the hijacked ship would be sailed to either Haradheere or Hobyo.

Monday's hijacking brings to six the total number of vessels currently in the hands of Somali pirates.

Joel Morgan, the Seychelles' minister of state for piracy, said maritime traffic in the area had dropped by a third recently due to the threat.