Kalaburugi Superintendent of Police N Shashikumar told PTI that those arrested were identified as Lakshmi, Athera and Vishnupriya.
All of them have been sent to judicial custody, he said.
Nineteen-year-old Aswathi was allegedly force-fed toilet cleaner by her seniors at the hostel of Al Qamal College of Nursing in Kalaburigi on May 9, seriously damaging her internal organs.
Based on her statement, police in Kozhikode had registered an FIR on June 22 against five of her seniors.
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National Human Rights Commission took cognizance of media reports of the incident and asked the state government and Kozhikode district authorities to file a report on it and action taken.
It issued notices to the Chief Secretary and Director General of Police, Karnataka, as well as the District Collector and Superintendent of Police of Kozhikode, calling for reports on action taken in the matter within four weeks.
NHRC said the Apex Court has also referred to ragging as an ugly scar, which needs to be obliterated from educational institutions. The college authorities were legally bound and responsible to ensure protection of students from the menace of ragging, the Commission stated.
A Karnataka police team probing the incident is now in Kozhikode and will visit her tomorrow to record her statement.
Kerala Women's Commission also wrote to its counterpart in Karnataka, urging it to intervene in the matter.