The first explosion was reported in a church located in the capital.
In just one church, St. Sebastian's in Katuwapitiya, north of Colombo, more than 50 people had been killed, a police official told Reuters, with pictures showing bodies on the ground, blood on the pews and a destroyed roof.
The blasts occurred at around 8:45 am as Easter Sunday masses were in progress, police spokesman Ruwan Gunasekera told Reuters.
Photographs of disorientated crowds have emerged from the explosions at in Kochchikade St Anthony's church in Colombo and the Zion Church in Batticaloa.
Colombo National Hospital Director Samindi Samrakoon said she knew of at least 20 deaths and 280 people injured.
There have been no immediate claims of responsibility, but one official said the church attacks are suspected of being carried out by suicide bombers.
"A bomb attack to our church, please come and help if your family members are there", read a post in English on the church's Facebook page.
"Pakistan condemns explosions and terrorist attacks in Sri Lanka at churches and hotels, that have led to numerous casualties and vast loss".
He said he had been to two of the attacked hotels and was at the scene at St Anthony's Shrine, where he described "horrible scenes".
Sources said that there were 62 casualties in Negombo, while 42 people had died at the National Hospital.
Sri Lankan security officials say they are checking for details. It was unclear whether there were any casualties in the hotels. Over 400 others have also sustained injuries in six simultaneous blasts in the South Asian country on Easter Sunday. He said,"I strongly condemn the cowardly attacks on our people today".
Sri Lanka is a majority-Buddhist country, with 6 per cent of the population adhering to the Catholic faith. "I call upon all Sri Lankans during this tragic time to remain united and strong", he said in a Tweet.
An emergency meeting has been called by Prime Minister Ranil Wickremesinghe in view of the blast and 200 troops of Army have been deployed in the affected area. "The government is taking immediate steps to contain this situation".
Sri Lanka blasts LATEST updates: A seventh blast has been reported in a suburb of Sri Lanka's capital, Colombo.
Out of Sri Lanka's total population of around 22 million, 70 percent are Buddhist, 12.6 percent Hindu, 9.7 percent Muslim and 7.6 percent Christian, according to the country's 2012 census.