Kolkata - A passenger train ploughed into a herd of elephants in eastern India, killing seven, including two calves, as they lumbered across the tracks in a forest, authorities said on Thursday.The crash was the worst of its kind in recent memory, said Hiten Burman, forestry minister in West Bengal. Ten other elephants were seriously injured and the death toll could rise, he said.The train was travelling at 80km/h through the Chapramari Forest when it struck the herd of 40 elephants crossing the tracks on Wednesday at dusk, Burman said."The herd scattered, but returned to the railway tracks and stood there for quite some time before they were driven away by forest guards and railway workers who rushed to the spot after the accident," he said.Burman said railway authorities have ignored requests from his department to have trains reduce their speeds inside the elephant corridor in Jalpaiguri district, about 670km from Kolkata, the state capital.Dozens of elephants have died in recent years after being struck while crossing railway tracks that run through India's national parks and forests. In December, a train killed five elephants in neighbouring Orissa state."It is an irony that elephants are being killed by speeding trains in north Bengal on regular intervals, even though it has been declared as the heritage animal in India and an elephant cub is the mascot of Indian Railways," said Animesh Basu, a wildlife activist and coordinator of the Himalayan Nature and Adventure Foundation.Basu, who blamed unrestricted movement of trains for the accident, said at least 50 elephants have been killed by trains since 2004 in West Bengal state.India's wild elephant population was recently estimated at about 26 000.