Katie Gee and Kirstie Trup, both 18 and from London, were working as volunteer teachers on the island.
Their mothers, Nicky Gee and Rochelle Trup, said they expected them to return to the UK on Thursday night.
The Foreign Office said it was “concerned to hear of an attack on two British nationals” and was “providing consular assistance”.
The women’s mothers said in a statement: “Both families are extremely upset and distressed at this completely unprovoked attack on their lovely daughters who had only gone to Zanzibar with good intention. We understand that they will be flying home overnight.
“We appreciate all the interest and support we have received from the media but we would ask that we are left alone until we have been reunited with our daughters.”
Read more: http://www.bbc.co.uk/news/uk-23611840