Four persons, identified as Y Manao Singh (52), Sanabanta Das (22), Akoijam Ongbi Sanajaobi Devi (55) and Ningombam Manisam Devi (65) were injured and taken to a nearby district hospital.
Their condition was stated to be critical, the sources said.
Three powerful bombs exploded in the capital complex in Imphal while Manipur Chief Minister O Ibobi Singh was giving his speech at the 1st Manipur Rifles parade ground where the main celebrations was taking place.
The ground is situated only about 2 km away from the site of the bomb explosions.
The chief minister was appealing to insurgents to give up arms and join the national mainstream by participating in the development process.
Sources said a powerful bomb, allegedly planted by the insurgents at the side of busy road at Sagolband in the capital complex, was apparently set off by using a remote-controlled device around 9 am, damaging the wall of a nearby house. They said the bomb might have been planted to attack security personnel who used the road often to go to the Central Reserve Police Force headquarters at Langjing, about 6 km west of Imphal.
Ten minutes later, another powerful bomb exploded at a place on Minuthong bridge on Imphal river in the capital complex, sources said.
Official reports from Thoubal district said minutes after the bomb explosion at Mela ground, the police and para-military forces, including Assam Rifles personnel, surrounded nearby suspected areas and rounded up several persons. All the detained were later freed after proper verification, the reports said. Passers-by at isolated places were also checked to detect movement of ultras who sneaked into nearby interior areas after the explosion, reports said.
The third explosion occurred in the Mahabali Temple complex, about 1.5 km from the parade ground of 1st Manipur Rifles, at around 9.45 am, the sources said.
A major portion of the fencing wall of the temple was destroyed in the explosion.
No one was injured in the three explosions.
The police and security forces stepped up patrolling after the explosions at the capital complex and blocked all exit points to prevent escape of suspected insurgents who exploded the bombs.
Several areas were searched, but no arrest was made, the sources said. All police and security posts were given a red-alert signal to intensify security measures and patrol within their jurisdictions.
Official reports said Independence Day was celebrated amid tight security deployment at all district headquarters peacefully.
Ibobi Singh in his speech said there was no room for violence in a democratic country like India and asked the insurgents to sit for dialogue and discussion.
Major insurgent organisations, including the United National Liberation Front, Revolutionary People's Front, People's Revolutionary Party of Kangleipak, and Kanglei Yawol Kann Lup had earlier called for boycott of Independence Day celebrations, saying Manipur was "forcibly merged" with the Union in 1949.