The decision of emergency was taken at meeting of the National Security Council to empower the security forces and to ensure public security. The meeting also decided to declare Tuesday as a national day of mourning.
The security situation remains tense as a van carrying explosives was diffused near the Colombo church, which faced attack on Sunday.
Another explosive detonators were recovered in a market area as security agencies keep frisking sensitive areas to thwart repetition of attacks on Sunday which killed around 300 people.
Most of the shops and business establishments in Colombo and other areas remain closed and night curfew will be in place from 8 PM to 4 AM.
Earlier, the government said that a local religious group National Tawheed Jamaath is behind the attacks but such a small local group cannot organise attacks at such a level.
Addressing a press conference, cabinet minister and government spokesman Rajitha Senaratne said the international support behind the attacks is being investigated and they are trying to ascertain how suicide bombers were prepared. The minister said there were inputs from international intelligence agencies earlier warning of such suicide attacks and expressed regret that it could not be avoided. The minister also added that a detailed security check out is being carried out at all sensitive places across the country as there are inputs of more such attacks.