Prayag was the original name of Allahabad, one of the oldest cities of UP.
Allahabad will be called Prayagraj from today, Uttar Pradesh Minister Siddharth Nath Singh said after a cabinet meeting in which the plan was cleared.
Chief Minister Yogi Adityanath had announced days ago that the historic Uttar Pradesh city would become "Prayagraj" as it was what people "wished".
The saffron-robed chief minister wanted the new name in place before the annual Kumbh Mela, a mega spiritual gathering that brings thousands from across the nation to Allahabad, which features the holy confluence of the rivers Ganga, Yamuna and the mythical Saraswati.
"The renaming of Allahabad as Prayagraj before Kumbh came for approval in the meeting and I am happy to say Allahabad will now be known as Prayagraj," Siddharth Nath Singh told reporters.
Justifying the decision, the minister said the name "Prayagraj" appears in ancient texts like the Rig Veda, Mahabharat and Ramayana.
"The people of Allahabad, the sages and seers wanted that Allahabad should be known as Prayagraj. Two days back, when the chief minister had chaired a meeting pertaining to Kumbh there, he had himself mooted that Allahabad should be called Prayagraj. All the sages and seers had given their unanimous approval," said Mr Singh.
There have been mixed reactions to the rechristening; critics say there have been quite a few name-changes over the past few years and they appear to be an attempt to distract attention from the fact that there has been no real change on the ground.
Congress leader Onkar Singh said the region where the Kumbh takes place is already called the "Prayag (confluence)". If the government wanted, it could make Prayagraj a separate city without any name-change, he suggested.
The Congress leader also pointed out that Allahabad was a repository of history, the venue of pre-independence meetings where the freedom movement took shape and where India's first prime minister Jawaharlal Nehru was born.
Prayag was the original name of Allahabad, one of the oldest cities of UP. It was named "Illahabad" or "abode of God" by Mughal emperor Akbar in 1575.
Recently, the UP government renamed the Mughalsarai Railway station, another historic spot, to Deen Dayal Upadhyaya junction.