At least 137 people were killed and hundreds injured when a string of blasts ripped through high-end hotels and churches as worshippers attended Easter services.
The fatalities include at least 45 people killed in Colombo, where three hotels Shangri La, Cinnamon Grand and Kingsbury and a church were hit.
Another 67 were killed in an attack on a church in Negombo north of the capital, with another 25 dead at a church in the town of Batticaloa, in the east of the country.
A police official said at least nine foreigners are among those killed in Sri Lanka blasts.
The nature of the blasts was not immediately clear and there were no immediate claims of responsibility.
President Maithripala Sirisena in an address said he was shocked by the explosions and appealed for calm.
Finance Minister Mangala Samaraweera, writing on his verified Twitter account, said the attacks had killed "many innocent people" and appeared to be a "well-coordinated attempt to create murder, mayhem & anarchy."
The first explosions were reported at St Anthony's Church in Colombo and St Sebastian's in the town of Negombo just outside the capital.
At least 160 people injured in the St Anthony's blast had been admitted to the Colombo National Hospital by mid-morning, an official told AFP.
The blasts hit the two churches as worshippers attended Easter services, police said.
Shortly after those blasts were reported, police confirmed three hotels in the capital had also been hit, along with a church in the town of Batticalao, in the east of the country.
An official at one of the hotels, the Cinnamon Grand Hotel near the prime minister's official residence in Colombo, told AFP that the blast had ripped through the hotel restaurant.
He said at least one person had been killed in the blast.
An official at the Batticaloa hospital told AFP more than 300 people had been admitted with injuries following the blast there.
"A bomb attack to our church, please come and help if your family members are there," read a post in English on the Facebook page of the St Sebastian's Church at Katuwapitiya in Negombo.
Sri Lankan Prime Minister condemned the attack and wrote on Twitter, "I strongly condemn the cowardly attacks on our people today. I call upon all Sri Lankans during this tragic time to remain united and strong. Please avoid propagating unverified reports and speculation.
The government is taking immediate steps to contain this situation."
"Emergency meeting called in a few minutes. Rescue operations underway," Sri Lanka's Minister of Economic Reforms and Public Distribution, Harsha de Silva, said in a tweet on his verified account.
He said he had been to two of the attacked hotels and was at the scene at St Anthony's Shrine and described "horrible scenes."
"I saw many body parts strewn all over," he tweeted, adding that there were "many casualties including foreigners."
"Please stay calm and indoors," he added.
Photos circulating on social media showed the roof of one church had been almost blown off in the blast.
The floor was littered with a mixture of roof tiles, splintered wood and blood.
Several people could be seen covered in blood, with some trying to help those with more serious injuries.
There were no immediate claims of responsibility.