The area where the bomb went off is close to the official residence of Chief Minister Okram Ibobi Singh.
"A powerful bomb was exploded near the deputy commissioner's office in the eastern part of the Imphal city Sunday morning," said a police spokesperson.
Police officials with additional reinforcement have rushed to the spot.
A combing operation was launched to nab the guerrillas who set off the blast.
"It was not yet clear whether the bomb was planted or hurled from the nearby areas," the police official said.
The area where the bomb went off is close to the official residence of CM.
Police said the militant outfit behind the blast was not yet confirmed.
Army soldiers Saturday recovered two Improvised Explosive Devices (IEDs) planted at separate places of Manipur's Bishnupur district. Both IEDs were safely defused.
Security was further stepped up at strategic locations, including crowded commercial areas of Ima Market, Paona Bazaar, Thangal Bazaar and Governor Road and civil secretariat areas in Imphal.
Police have also enhanced frisking and patrolling in and around the Imphal city.
Six frontline separatist outfits based in Assam, Manipur, Meghalaya and Tripura earlier gave a call to boycott the Republic Day celebrations and asked people to observe a general strike from 1 a.m. to 5 p.m. Jan 26.
Separatist rebel groups in the northeast have for years boycotted national events and have staged violent attacks in the run-up to the celebrations to make their presence felt.