"Odisha will observe one-day state mourning tomorrow in honour of late Rabi Ray," an official statement issued by Chief Minister's office said.
The National Flag will be flown at half-mast across all government buildings for the day, the statement said adding that the body of the departed leader will be cremated with full state honour tomorrow.
Earlier at about 3 pm, Ray breathed his last while undergoing treatment at SCB Medical College Hospital in Cuttack.
Hundreds of people rushed to the hospital and later to his Kalyan Nagar residence in Cuttack to pay respect to the departed soul.
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Many also joined in the procession when his body was taken to his alma mater, Ravenshaw University and MS Law College in Cuttack.
Prime Minister Narendra Modi, Chief Minister Naveen Patnaik and State Governor S C Jamir along with several other leaders across the country sent their condolences.
Ray's political career began from Cuttack when he
became President of students' union of both these famous institutions in late 40's. The socialist leader was loved and respected by leaders cutting across party lines.
Inspired by Rammohan Lohia, he founded Socialist Party in Odisha in 1956 and later went on to become the national secretary of the Party in 1960.
He was first elected to the Lok Sabha in 1967 from Puri parliamentary constituency and was the leader of Samyukta Socialist Party in the Lok Sabha.
In 1974, he was elected to Rajya Sabha from the State and was made a cabinet minister in 1977 by the then Prime Minister Morarji Desai when Ray was functioning as one of the secretaries of Janata Party.
Besides his notable political contributions, Ray was also actively associated with several sociocultural organisations including Lohia Academy and Gram Vikash Foundation till he was indisposed due to old age.
A true socialist by nature, Rabi Ray has also contributed immensely to the field of literature.