A woman in her 90s is in a "potentially life-threatening" condition after being bitten by a dog, police say.
Devon and Cornwall Police said officers were called to a property in Cannis Road, St Austell, Cornwall, at 00:45 BST on Thursday, following the attack.
Police said a woman was taken to Derriford Hospital, in Plymouth, with a "serious dog bite to her arm".
The dog - which was not a banned breed - was put to sleep and a man in his 60s from St Austell has been arrested on suspicion of causing or allowing a vulnerable adult to suffer serious harm, the force added.
Police said her next of kin had been informed.
Officers said: "This is believed to have been an isolated incident with no wider risk to the community.
"A police cordon remains in place while inquiries are continuing."