The man holding a two-year-old girl in an armed siege is believed to be her father, Thames Valley Police said.
Officers were called to a house in Kidlington, Oxfordshire, at 3:40am this morning following reports a 38-year-old man was holding twin girls in a "domestic-related incident", the force said.
The unnamed man is estranged from the children's mother and does not live at the property in Morton Avenue.
Thames Valley Police said: "The man has been in regular communication with the police and one girl was released at around 9:45am.
"Officers are continuing to speak to the man who is still inside the property with the other child".
Armed officers were deployed to the address and a cordon has been placed around the property.