St. Sebastian's Church posted photos of the aftermath on Facebook, pleading for relatives to "come and help if your family members are there."

Harsha de Silva, Sri Lanka's minister of economic reforms and public distribution, said he visited the churches, and he described the horrific scenes. "I saw many body parts strewn all over. Emergency crews are at all locations in full force," he said on Twitter.

"It was a river of blood," a shopkeeper named N.A. Sumanapala near St. Anthony's Shrine told The New York Times. "Ash was falling like snow," he said. "I saw limbs and heads. There were children too."

Sri Lankan resident Usman Ali said an overwhelming number of people arrived at the national blood center to help. "It's so overcrowded they cannot control the crowd," he tweeted. "Currently they are sending back people who have come after taking down name, contact and blood group."

The government announced a curfew after the explosions, which took immediate effect. It also chose to block social media sites, including Facebook and Instagram, to stop the spread of false information. The Sri Lanka Red Cross said false informationhad already begun to spread online about its building being attacked and sought to dispel the rumor.

Sri Lanka's president, Maithripala Sirisena, issued a statement calling for people to remain calm and support the authorities in their investigations, according to the BBC.

Prime Minister Ranil Wickremesinghe said the government is taking immediate steps to contain the situation. "I strongly condemn the cowardly attacks on our people today," he said. "I call upon all Sri Lankans during this tragic time to remain united and strong."

Finance Minister Mangala Samaraweera tweeted that the bomb blasts seemed "to be a well coordinated attempt to create murder, mayhem and anarchy."

The foreign minister said at least 27 foreigners were killed. A Portuguese national, a Dutch national, two Turkish engineers, at least three British citizens and several Chinese citizens were reported among the dead.

It remains unclear whether any Americans were among the dead or wounded. A State Department spokesman was not immediately available for comment. The U.S. Embassy in Colombo gave Americans who might need help a phone number to call to reach embassy staff.

During his Easter Sunday mass at the Vatican, Pope Francis took time to offer condolences to victims of what he called "such a cruel act of violence."

President Trump tweeted a message of support for Sri Lanka on Sunday morning,saying, "The United States offers heartfelt condolences to the great people of Sri Lanka. We stand ready to help!"

NPR's Lauren Frayer reports that the violence comes just before the 10-year anniversary of the end of Sri Lanka's civil war.

This is a developing story. Details may change as more information becomes available.