At least 30 people, including children, have been killed and dozens more injured after an express train derailed in northern India, authorities said.

Television images showed two mangled carriages lying beside the track after the accident on Friday, which occurred about 50km from Lucknow, capital of the northern state of Uttar Pradesh.

Neeraj Sharma, chief public relations officer for Northern Railway, told the AFP news agency that the rescue work had been completed by early afternoon. Sharma said 50 people received injuries in the crash.

An official at the scene said one of the coaches was vacant at the time of the accident, limiting the number of deaths.

The Press Trust of India (PTI) news agency said the train apparently overshot a signal before crashing into a barrier and coming off the rails.

Sharma said there would be an official investigation into the cause of the accident, which could have been down to driver negligence or the brake system failing.

India's Railways minister expressed his grief at the loss of life and promised to expedite the process of modernising the country's rail infrastructure.

Source: Agencies