Sussex Police confirmed officers were called to support the fire and ambulance services at a house fire Dorset Place, Worthing, at around 10.45am today (Wednesday, December 1).
"A 99-year-old local woman was treated by paramedics at the scene, but was sadly pronounced dead," a police spokesperson said.
"Her next of kin have been informed.
"An investigation into the exact cause of the fire is ongoing, but there do not appear to be any suspicious circumstances."
High Street was closed from the junction with Rectory Road but it has now been reopened, police said.