Hundreds of Google staff have signed a letter backing a leading AI ethics researcher who was sacked by Google.

Timnit Gebru says she was fired after sending an internal email that accused Google of "silencing marginalised voices".

Hundreds of colleagues have signed a letter accusing the search giant of racism and censorship, while Twitter users have rallied around Dr Gebru using the hashtag #BelieveBlackWomen.

Google disputes her version of events.

Dr Gebru is a well-respected researcher in the field of ethics and the use of artificial intelligence.

She is well-known for her work on racial bias in technology such as facial recognition, and has criticised systems that fail to recognise black faces. 

Her co-author on one of those well-known papers, Joy Buolamwini, said Dr Gebru "deserved more" from Google.

"Ousting Timnit for having the audacity to demand research integrity severely undermines Google's credibility for supporting rigorous research on AI ethics and algorithmic auditing," she said.

"We owe her a debt of gratitude for advancing not just the field of artificial intelligence, but for advancing equality with humility and grace."