At least 45 people have been killed after 14 carriages of an Indian express train derailed in northern Uttar Pradesh state, reports say.

The incident took place on the Indore-Patna Express just after 03:00 local time on Sunday (21:30 GMT Saturday) near the city of Kanpur.

The death toll is expected to rise as rescuers continue to work through the wrecked carriages.

More than 100 people have been reported injured.

It was not immediately clear what caused the coaches to derail.

Krishna Keshav, who was travelling on the train, told the BBC: "We woke with a jolt at around 3am. Several coaches were derailed, everybody was in shock. I saw several bodies and injured people."

Most of the victims were located in two carriages near the engine which overturned and were badly damaged, reports said.

Rescue workers at the site were using heavy machinery to cut through the carriages to reach survivors.

Indian prime minister Narendra Modi tweeted: "Anguished beyond words on the loss of lives due to the derailing of the Patna-Indore express. My thoughts are with the bereaved families.

"Prayers with those injured in the tragic train accident."

Mr Modi said he had spoken to Railways Minister Suresh Prabhu, who was "personally monitoring the situation closely".

On his own Twitter account, Mr Prabhu warned that "strictest possible action will be taken against those who could be responsible for accident".

He said an investigation into the crash would begin immediately and compensation would be paid to "unfortunate passengers who died and to injured".

Home Minister Rajnath Singh said that India's National Disaster Response Force was overseeing the rescue efforts.

Kanpur is a major railway junction and hundreds of trains pass through it every day.

Anil Saxena, a spokesman for the railway company, said trains were being diverted along other routes.

Train accidents are common in India, where much of the railway equipment is out of date. About 23 million passengers use the country's vast network every day.