AI chatbot company Replika, which offers customers bespoke avatars that talk and listen to them, says it receives a handful of messages almost every day from users who believe their online friend is sentient.

"We're not talking about crazy people or people who are hallucinating or having delusions," said Chief Executive Eugenia Kuyda. "They talk to AI and that's the experience they have."

The issue of machine sentience — and what it means — hit the headlines last month when Google placed senior software engineer Blake Lemoine on leave after he went public with his belief that the company's artificial intelligence (AI) chatbot LaMDA was a self-aware person.