Two British women were injured in an acid attack on the east African island of Zanzibar, off the coast of Tanzania, local police said. The attack was perpetrated by two men on motorcycles who fled the scene and didn't take anything.

The women were attacked in Stone Town, the island's historic center. They were in Zanzibar working as volunteer teachers, according to travel firm i-to-i Travel.

Stone Town is a UNESCO world Heritage Site that is popular with tourists. The attack occurred on Wednesday night as the women were walking along the street, said Muccadam Khamis, the police commander.

The women were brought to a local medical center where they received first aid treatment. They then went to Dar es Salaam with the aid of British consular officials, where they received hospital treatment.

"We are concerned to hear of an attack on two British nationals in Zanzibar on 7 August," a Foreign Office spokesman said. "We are providing consular assistance and are in contact with the Tanzanian authorities."

The women have been discharged from the hospital. The travel company is working to help them return home.

"The motive for the incident is as yet not known and we will await the report from the local authorities in Zanzibar before any comment can be made," a statement from the travel company said. "The safety of our customers is of paramount importance to us and our own investigation will be launched as soon as it is possible to do so."

The company aims to provide young travelers with "meaningful travel trips" by placing them in volunteer positions with community projects internationally. They provide volunteer tourism services.

The trips last from two to eight weeks, according to the web site. The women were teaching English in Stone Town.

Zanzibar is a semi-autonomous par of Tanzania.