How Odisha train accident happened?

Over 275 people were killed and more than 900 injured after a horrific three-train collision last evening in Odisha’s Balasore.
The incident took place when a passenger train, the Coromandel Shalimar Express, derailed and hit a goods train, and another train, the Yesvantpur-Howrah Superfast, crashed into the derailed coaches.
“Two passenger trains had an active involvement in the accident while the third train, a goods train, which was parked at the site, also got (involved) in the accident,” Amitabh Sharma, executive director, Indian Railways, said
The Coromandel Shalimar Express, heading to Chennai, reportedly derailed and hit a goods train, after which many coaches flipped over.
The Yesvantpur-Howrah Superfast then collided with the derailed coaches. Both trains were moving at a high speed when the collisions took place.