Airbnb on Friday said it is cracking down on racism after booting one home-sharing host for blatantly discriminating against a woman of color who had made a reservation.

A freshly launched review of how hosts and guests interact online and in the real world should be completed by September, when the San Francisco-based startup will announce the findings and what it will do about them.

"We have a zero tolerance policy for discrimination and when we become aware of it we take action," Airbnb said in a letter to members.

Airbnb said that it has enlisted former American Civil Liberties Union head Laura Murphy to lead its discrimination-fighting efforts.

"Racial discrimination is unacceptable and it flies in the face of our mission to bring people together," Airbnb said in an email response to an AFP inquiry.

The high-profile campaign to ferret out discrimination at the popular home-sharing service came after an Airbnb host in the US state of North Carolina fired off hateful, race-based messages to a black woman while canceling a stay she had booked at his home.

Airbnb told AFP it was "horrified" by the messages. The host was removed from the service, while the guest was ensured a safe place to stay, according to the startup.

"The incident in NC was disturbing and unacceptable," Airbnb chief executive Brian Chesky said in a message posted at his @bchesky Twitter account.

"We have permanently banned this host."

Complaints of racism by Airbnb hosts are not new, having given rise to an #Airbnbwhileblack hashtag used for commenting on the topic at Twitter.

An African-American man last month filed a US lawsuit against Airbnb based on racial discrimination by hosts.

Airbnb said that it has been fighting the problem with offerings such as unconscious bias training for employees and hosts.