Questions are being asked about what warnings authorities had about a spate of bombings in Sri Lanka and if more could have been done to protect the main targets of the attacks — Christians celebrating Easter and tourists.

A series of devastating explosions ripped through luxury hotels and churches holding Easter services on the island nation, killing at least 207 people and injuring 450 more.

The explosions were concentrated in the capital city of Colombo but also included blasts at Negombo and Kochchikade, north of the city, and Batticaloa in the east of the country.

Sri Lanka's Telecommunications Minister Harin Fernando took to Twitter with an image that he claims showed a memo warning of a possible attack headed "information of an alleged plan (sic) attack".

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Dated April 11, and written in Sinhalese with some English, it includes a reference to National Thowheeth Jama'ath (NTJ), a radical Muslim group in Sri Lanka.

"Some intelligence officers were aware of this incidence … Serious action needs to be taken as to why this warning was ignored," Fernando wrote.

The country's Prime Minister Ranil Wickremesinghe has acknowledged that there was some "prior information" of a possible attack but he told reporters those concerns had not been passed onto ministers.

AFP has reported that police chief Pujuth Jayasundara sent a warning to senior officers 10 days ago that suicide bombers from the little-known Islamist group could attack "prominent churches".

The memo reportedly said: "A foreign intelligence agency has reported that the NTJ is planning to carry out suicide attacks targeting prominent churches as well as the Indian high commission in Colombo".

Sri Lankan Army soldiers secure the area around St Anthony's Shrine after a blast in Colombo. Photo / AP
Sri Lankan Army soldiers secure the area around St Anthony's Shrine after a blast in Colombo. Photo / AP

The identities of some of the first victims are emerging including five Britons, three of who may have died in the queue for a breakfast buffet in a major hotel. One victim shared a tragic last selfie to social media moments before a bomb exploded.