The incident took place in Shamli, around100 km from the national capital, on Tuesday evening when the sisters, three of whom are teachers, were returning home from a government school.
"The victims were walking together when two men on a motorbike made lewd remarks and the man who was riding pillion splashed acid on all of them," Abdul Hammed, senior police officer who is investigating the case said. Mr Hameed said no arrests had been made and the motive behind the crime was unclear.
The youngest sister, he said, suffered maximum burn injuries and had to be rushed to a hospital in Delhi.
Attacks on women have topped the national agenda since December 2012 when a medical student was assaulted and raped by six men on a moving bus in Delhi. She died two weeks later of her injuries.
Acid attackers can be jailed for eight-12 years depending on the injuries inflicted, but the offence is bailable.
Activists have asked that India should regulate the sale of an acid called "Tezaab" which is designed to clean rusted tools but is commonly used in attacks.
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