Old design submarines still used by China
An accident on board a conventionally-powered submarine off China's coast has killed all 70 officers and crew, the country's official news agency has reported.
The accident is said to have occurred in Chinese territorial waters east of the Neichangshan islands in "recent days".
The news agency said the submarine was on a training exercise when it encountered "mechanical problems", and the vessel had been towed to an unidentified port.
No specific date or other details were given.
It is the worst submarine accident since August 2000, when the Russian nuclear-powered Kursk sank with its 118 crew in the Barents Sea.
It is also one of the worst naval accidents in Communist China's history, according to military sources.
The Chinese Central Military Commission has sent its condolences to families of officers and crew.
The BBC's Rupert Wingfield-Hayes, in Beijing, says the report by China's state-run media leaves many questions unanswered.
It remains unclear why none of the crew were able to escape, why the boat was recovered so quickly, and exactly when and where the accident took place.
Our correspondent says that given the Chinese military's notorious secrecy, it's perhaps not surprising that the information is vague.
The vessel is believed to be of the Ming class, built from Soviet designs based on German submarines dating back to World War ll.
While these boats are entirely obsolete by modern standards, they are a relatively inexpensive option for patrol and coastal defence duties, and construction is still going on.
The Chinese were reportedly negotiating with Russia last year to buy eight 636 Kilo-class vessels, equipped with anti-ship missile systems, in a $1.6 bn deal.
According to reports, China's own submarine manufacturing programme is in difficulty, particularly its efforts to develop the Song class guided-missile submarine.
Jane's Defence Weekly says the first Song started sea trials in 1995, but proved a failure.
China's navy has also reportedly experienced operating problems because of inadequate crew training.
Intelligence reports say Beijing increased military spending last year to $20 bn.