Katie Gee and Kirstie Trup, both 18, are recovering after the attack by men on a motorbike as they walked along a road on the island and they are due to leave the country this evening.
The teenagers, from north London, were in the last week of a trip as volunteer teachers to the predominantly Muslim island, when men on a moped reportedly threw a corrosive substance at their heads and chests.
The attack has raised fears that the girls were the victim of a religious attack after Miss Trup was set upon by a Muslim woman two weeks earlier for singing during Ramadan. The pair were also teaching at a primary school affiliated with the Anglican church.
One of their friends, Oli Cohen, 21, told the Telegraph: 'She was shocked as it just came from out of the blue - but she wasn't scared enough to come home. She stayed out there to finish her trip and volunteering.' The pair's mothers, Nicky Gee and Rochelle Trup, are said to be 'extremely upset and distressed' over the attack on their daughters.
Family friend Doug Morris read a statement from the two mothers outside Kirstie's family home in Hampstead Garden Suburb today. He said: 'Both families are extremely upset and distressed at this completely unprovoked attack on their lovely daughters who went to Zanzibar with good intentions. 'We understand that they will be flying home overnight.'
Speaking outside the Hampstead Garden Suburb mansion Kirstie lives in with her dad Marc and mum Rochelle, another friend added: 'They are in the end game now, it has been a bit fraught liaising with the insurance company and consul. 'We think the medevac flight is organised. The latest information is they are going to be leaving Dar es Salaam in a couple of hours, maybe three hours. 'They have got to do it in three four-hour flights. It is a long haul.
'The number one priority is getting them back, I think they are pleased to be coming home.'
He said both sets of parents had spoken to their daughters and asked if it was emotional said 'yes'.
He added: 'I can't comment on the medical treatment, we just wanted to get them home, get them seen and get them treated.' The girls were attacked as religious tension between Christians and Muslims on the paradise island continues to rise.
The semi-autonomous region of Tanzania is predominantly Muslim and has been the scene of some religious violence in recent years. Last November a cleric was hospitalised in an acid attack and two Christian leaders were killed earlier this year. Five churches were also torched last year.
Mkadam Khamis, a police commander on the island, told the Associated Press the women were teaching at a primary school affiliated with the Anglican Church. Police refused to link the attack with the rising religious tensions.
Tanzania President Jakaya Kikwete described the attacked as 'shameful' after visiting the girls in hospital.
Ms Trup is from affluent Hampstead and Ms Gee was formally a student at the Francis Holland School in Chelsea.
Ms Gee's mother Nicky said the families are fighting to get the two women home as soon as possible.
The women were on a trip organised by i-to-i Travel, which is based in Tunbridge Wells, Kent, and runs gap year trips to parts of Africa, Asia, central and South America and Australia.
Trips to teach in Zanzibar, based in Stone Town, start at £669 for two weeks, according to its website.
In a statement, i-to-i Travel said they had been released from a hospital in the Tanzanian capital, Dar es Salaam, where they had been flown for medical treatment after the 'acid attack'.
'All our efforts remain focused on ensuring they are supported whilst assisting them and their relatives with the arrangements for their return home.' it said.
The Foreign Office travel advice for Tanzania warns that although most visits to the country are trouble-free, 'violent and armed crime is increasing'.
The advice, available on its website, says: 'Mugging, bag snatching (especially from passing cars) and robbery have increased throughout the country.'
It adds: 'In Zanzibar incidents have taken place in Stone Town and on popular tourist beaches.'
Jakaya Kikwete, Tanzania's president, is reported to have visited them at the Aga Khan Hospital in Dar es Salaam and promised that the men responsible for the 'shameful' attack would be found.
The pair were in the final week of their three week trip volunteering with the NGO Art in Tanzania.
Television images showed one girl obviously in pain in the back of a car at the Zanzibar airport.
They were flown to hospital in Dar es Salaam, Tanzania, and have since been discharged and police say the women were lucky to escape serious burns.
A spokesman for Art in Tanzania said representatives were today at the Aga Khan Hospital to help the girls, who were also being interviewed by Foreign Office officials and again by police.
Tanzania President Jakaya Kikwete visited the two women at the Aga Khan Hospital today.
On arrival at the hospital, the president, surrounded by bodyguards, urged the police to step up their investigation and catch the culprits. He said: 'This puts the name of our country in the bad-books.' He also praised the hospital for its efforts in looking after the girls.
Zanzibar Assistant Commissioner of Police Mkadam Khamis told The Evening Standard: 'The doctors said the injuries are relatively minor. There is discolouration but they are not expected to be scarred. It is very fortunate.' The pair had been volunteering at a local school with the organisation i-to-i Travel.
A spokeswoman said: 'There is a chance that attacks could happen again and we are making sure people are fully aware of the protection procedures.' The company said in a statement: 'All our efforts remain focused on ensuring they are supported whilst assisting them and their relatives with the arrangements for their 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. 'The female clients had been volunteer teachers on Zanzibar and were in the final week of their trip.'
Deputy police commissioner Mkadam Khamis said: 'Police in Zanzibar have launched a manhunt, and we ask for public assistance in identifying the attackers. 'The motive for the attack on the volunteers, aged 18 years, has not been established.'
Mr Khamis Mkadam said: 'The incident occurred when the streets were deserted as most people were breaking their Ramadan fast.'
Zanzibar, a paradise island around 22 miles off the coast of east Africa, and part of the republic of Tanzania, attracts thousands of British tourists a year.
Police on the island say it is the first time a tourist has been attacked in this way.
However, there have been concerns that religious tension in Zanzibar have increased in recent months.
Said Ali Mbarouk, Minister of Information, said: 'We should cooperate with other government sectors to ensure that the perpetrators are arrested and brought to justice.
'I beg our nationals in any way this is not something they should be doing because tourism is the strong pillar of our economy so if we do such acts we are killing our economy and our livelihoods in general so it is not an honourable thing to do it's a bad thing and it's supposed to be condemned by all citizens of Zanzibar.'
The police described the attack as 'an isolated incident', refusing to link it to rising religious tension on the island between majority Muslims and its Christian population.
Dr Mike Jennings, a lecturer at the School of Oriental and African Studies in London, said Muslim group called Uamsho, which translates as 'The Awakening', was a political rather than terrorist organisation and had no known links to Al Qaeda.
He said they want an independent Zanzibar and to introduce Islamic law on the island.
Dr Jennings said: 'It is political with a religious tone. Some people see it is as terrorism, but I don't think it is.
'Maybe this group was behind the attack, although it is too early to say.'
The majority of islanders are Muslim, with Christians making up as little as five per cent of the population.
A spokeswoman for the Foreign Office said: 'We are aware of an incident and are providing consular assistance.'
She added that officials became aware of the incident last night.