Pictures circulating on social media show part of a building has collapsed following a loud blast.
Thames Valley Police and a hazardous response team are at the scene.
A tweet sent out by Thames Valley Police said: “Officers are at Didcot Power Station at an incident with other emergency services.
“Futher details will be released in due course.”
Witnesses say an air ambulance has landed at the site.
A huge fire at Didcot power station destroyed four cooling towers in 2014.
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