At least 11 persons, including two children, were wounded in a grenade blast at a fairground in the state capital on Friday night, police said.
Hospital sources said some of the injured were discharged after first aid while some sustained critical injuries.
Police said two youths in a scooter hurled the China-made hand grenade at the fair venue in Tera and fled.
Police personnel from the nearby police station rushed to the site. However, no arrest could be made.
The fair is organised by the North East Mela Association ahead of the Ningol Chakkouba, the biggest social festival in Manipur to be held next week.
Gitchandra Leishangthem, secretary of the NEMA, said: "The fair was to be opened formally from Sunday morning. Entrepreneurs were busy installing their items and hoardings on Friday night in their stalls when the blast took place."
No group has claimed responsibility for the blast.
Though the organisers have not closed down the fair the entrepreneurs are having second thoughts over the growing sense of insecurity.
In view of the "improved law and order" in Manipur the government has been organising a fair twice a week from October 2 at Kangla park in the heart of Imphal city.
One bomb had been exploded not far from the venue last week. Besides a college located nearby was attacked with a grenade a few days back.
Reacting to the attacks, Chief Minister N. Biren Singh said "Persons who cannot tolerate the developmental works are resorting to senseless violence. However, people who ignore the disruptionist activities are going ahead."
Due to security concerns some families said they will abstain from visiting the fairs, including the one organised by the Manipur government at Kangla park.
The Armed Forces (Special Powers) Act, 1958 was imposed in Manipur on September 8, 1980. However, it was lifted from eight assembly segments in Imphal from August 12, 2004 following gang rape, custodial deaths and the naked protest by 12 women against the gang rape-cum-killing of T. Manoram by troopers of 17 Assam Rifles.