Banned insurgent outfit ULFA (Independent) later in the day claimed responsibility for the explosions.
Three of the explosions took place in Dibrugarh district and one in Charaideo, both in Upper Assam.
Additional director-general of police (law and order) G.P. Singh said: "We have been able to confirm four blasts. The first blast was reported at 8:10 a.m. and the last one 8:25 am."
"There was no damage to property and no human injury or casualties."
The first blast was heard at Teok Haat in Sonari under Charaideo District, the second one occurred Ain the oil town of Duliajan near Duliajan Police Station in Dibrugarh district.
The two other blasts were reported in Dibrugarh at Marwari patty near Gurudwara on A T Road and close to Circuit House in Graham Bazaar.
The police rushed and cordoned off the blast spots. Bomb disposal squad members also reached the areas witin a short time.
According to a senior Dibrugarh district police officer, the blasts at Marwari Patty and Graham Bazar were triggered by IED devices.
CCTV footage available from the blast spot at Duliajan showed two motor-bike riders speeding away after lobbing a grenade.
Singh said they had initially received reports of five blasts, including one at Doomdooma in Tinsukia district.
But the police and bomb experts found no trace of any blast at Doomdooma.
Chief Minister Sarbananda Sonowal, who ordered an inquiry, described the incidents as "cowardly attempt to create terror on a sacred day".
"Strongly condemn the bomb blasts in a few places of Assam. This cowardly attempt to create terror on a sacred day only exhibits the frustration of the terror groups after their total rejection by the people. Our Govt will take the sternest action to bring the culprits to book," Sonowal tweeted.
In a press statement, signed by Lt Joy Asom of its Publicity Department, ULFA(I) claimed responsibility for the blasts.
The banned insurgent outfit had called for a "general strike" on Sunday, asking citizens not to participate in the Republic Day celebrations. The ultras had also asked the people not to venture outdoor.
( With inputs from IANS )