COLOMBO (REUTERS, AFP) - A blast hit near a church in Sri Lanka's capital Colombo on Monday (April 22) as police tried to defuse a new bomb found by the site, a police spokesman said.

There was no immediate information on injuries in the blast. The explosion happened around 50m from the St Anthony's Shrine, one of three churches targeted in a string of suicide bombs on Sunday that killed nearly 300 people.

Police also found 87 bomb detonators at the main bus station in Colombo, on Monday, a spokesman said. Security forces are carrying out searches across the island to find those behind the bombs.

Seven suicide bombers took part in Sunday's attacks that also wounded more than 500, a senior investigator said on Monday (April 22).

Two of the suicide bombers blew themselves up at the luxury Shangri-La Hotel on Colombo's seafront, said Ariyananda Welianga, a senior official at the government's forensic division.

The others targeted three churches and two other hotels.

A fourth hotel and a house in a suburb of the capital Colombo were also targeted, but it was not immediately known how the attacks were carried out.

"Still the investigations are going on," Welianga said.

The Easter Sunday attacks mainly took place during church services or at hotel breakfast buffets.

Four of the bombs went off at roughly the same time, at 8.45 am local time, with two others coming within 20 minutes. The explosions at the fourth hotel and the house were in the afternoon.

"Guests who had come for breakfast were lying on the floor, blood all over," an employee at Kingsbury Hotel, one of those targeted, said. "We just picked up everyone, dead or alive and evacuated them."

There was no claim of responsibility, but the government believes a local Islamist extremist group called the National Thowheeth Jama'ath (NTJ) was behind the attacks, government spokesman Rajitha Senaratne said on Monday.

Senaratne, who is also a Cabinet minister, added that the government was investigating whether the group had "international support".

Documents seen by AFP show Sri Lanka's police chief issued a warning on April 11, saying that a "foreign intelligence agency" had reported NTJ was planning attacks on churches and the Indian high commission.

Not much is known about the NTJ, a radical Muslim group that has been linked to the vandalising of Buddhist statues.

A police source told AFP that all 24 people in custody in connection with the attacks belong to an "extremist" group, but did not specify further. All 24 are Sri Lankans.

Sri Lankans accounted for the bulk of the dead and wounded Sunday's attacks, although government officials said 32 foreigners were killed, including British, US, Turkish, Indian, Chinese, Danish, Dutch and Portuguese nationals.

President Maithripala Sirisena will declare a nationwide emergency from midnight on Monday, his office said.

"The government has decided to gazette the clauses related to prevention of terrorism to emergency regulation and gazette it by midnight," the president's media unit said in a statement. It said the measure would be confined to dealing with terrorism and would not impinge on freedom of expression.

The government has imposed a new curfew from 8pm on Monday to 4am local time on Tuesday, according to the police. A Sunday night curfew was lifted on Monday morning.

The US State Department said in a travel advisory "terrorist groups" were continuing to plot possible attacks in Sri Lanka and targets could include tourist spots, transport hubs, shopping malls, hotels, places of worship, airports and other public areas.

The Sri Lankan military, who were clearing the route from Colombo airport late on Sunday in preparation for Sirisena's return from abroad, found a crude bomb near the departure gate, an air force spokesman said. They destroyed the device in a controlled explosion.

There were fears the attacks could spark a renewal of communal violence, with police also reporting late on Sunday there had been a petrol bomb attack on a mosque in the northwest and arson attacks on two shops owned by Muslims in the west.

Buddhist-majority Sri Lanka was at war for decades with ethnic minority Tamil separatists, but violence had largely ended since the government victory in the civil war, 10 years ago.

Sri Lanka's 22 million people include Christian, Muslim and Hindu minority populations.

The explosion at the house in the Colombo suburb occurred when security forces raided a house there on Sunday afternoon, several hours after the attack. Police reported an explosion at the house and said three officers were killed.

SOCIAL MEDIA BLOCKED

Traffic was uncharacteristically thin in normally bustling Colombo after the island-wide curfew was lifted. Soldiers with automatic weapons stood guard outside major hotels and the World Trade Centre in the business district, where the four hotels were targeted, a witness said.

Scores of people who were stranded overnight at the main airport began making their way home as restrictions were lifted.

The government also blocked access to social media and messaging sites, including Facebook and WhatsApp, making information hard to gather.

A British mother and son eating breakfast at the luxury Shangri-La hotel were among those killed, British media reported.

An Australian survivor, identified only as Sam, told Australia's 3AW radio the hotel was a scene of "absolute carnage". He said he and a travel partner were having breakfast at the Shangri-La when two blasts went off. He said he had seen two men wearing backpacks seconds before the blasts.

"There were people screaming and dead bodies all around," he said. "Kids crying, kids on the ground, I don't know if they were dead or not, just crazy."

There were similar scenes of carnage at two churches in or near Colombo, and a third church in the north-east town of Batticaloa, where worshippers had gathered for Easter Sunday services. Pictures from the scene showed bodies on the ground and blood-spattered pews and statues.

Dozens were killed in one of the blasts at the Gothic-style St. Sebastian church in Katuwapitiya, north of Colombo. Police said they suspected that blast was a suicide attack.

DOMESTIC FEUD

Prime Minister Ranil Wickremesinghe acknowledged on Sunday that the government had some prior information about possible attacks on churches involving a little-known Islamist group, but said ministers had not been told.

The apparent lapse could feed into a feud between the prime minister and the president. Sirisena fired the premier last year and installed opposition strongman Mahinda Rajapaksa in his stead. Weeks later, he was forced to re-instate Wickremesinghe because of pressure from the Supreme Court, but their relationship is still fraught as a presidential election nears.