He lined up for breakfast before unleashing terror: Everything we know about the attacks in Sri Lanka.

-With AAP.

A rash of bombings at churches and hotels on Easter Sunday in Sri Lanka has caused blood shed on a scale not seen since the country’s 26-year civil war, which ended in 2009.

At least 290 people, mostly Sri Lankans but also including dozens of foreign citizens, have been killed in the eight explosions with this number set to rise as the number of people injured sits at 500.

A ninth bomb was discovered at Sri Lanka’s main international airport, prompting a lockdown.

A large PVC pipe packed with explosives was found on the way to Bandaranaike International Airport and was diffused by explosives experts, an air force spokesperson told Bloomberg.

Seven people have been arrested and three police officers were killed during a raid on a house in Colombo on Sunday as the death toll rose past 200, police and local media said.

The eight explosions, including suicide bomb attacks, led to an immediate clampdown, with the government declaring a curfew and blocking access to major social media and messaging sites, including Facebook and WhatsApp.

More than 50 people were killed in St. Sebastian's gothic-style Catholic church in Katuwapitiya, north of Colombo with pictures showing bodies on the ground, blood on the pews and a destroyed roof.

People were seen carrying victims out of blood-spattered pews. Witnesses described powerful blasts, followed by scenes of smoke, blood, broken glass, alarms going off and victims screaming.

Media reported 25 people were also killed in an attack on an evangelical church in Batticaloa in Eastern Province.

The three hotels hit were the Shangri-La Colombo, Kingsbury Hotel in Colombo and the Cinnamon Grand Colombo.

The manager at the Cinnamon Grand Hotel in Colombo said the suicide bomber had checked into the five-star hotel the night before and waited in a queue for a breakfast buffet before setting off the explosion in a packed restaurant at 8.30am, killing himself and a number of guests.

The bomber had checked in under a false address, claiming he was in the city on business, before unleashing terror on one of the hotel's busiest days of the year, the Daily Mail reported.

Defence Minister Ruwan Wijewardene said seven people have been arrested following the series of explosions.

The explosions led to an immediate clampdown, with the government declaring a curfew and blocking access to most major social media and messaging sites.

"Altogether we have information of 207 dead from all hospitals. According to the information as of now we have 450 injured people admitted to hospitals," Police Spokesman Ruwan Gunasekera told reporters in Colombo.

The Shangri-La's second-floor restaurant was gutted in the blast, with the ceiling and windows blown out. Loose wires hung and tables were overturned in the blackened space.

Colombo resident Bhanuka Harischandra, a 24-year-old founder of a tech marketing company was going to the city's Shangri-La Hotel for a meeting when it was bombed on Sunday.

"People didn't know what was going on. It was panic mode," he described of the scene. "There was blood everywhere."

Most of the more than 200 killed were Sri Lankans. But the three hotels and one of the churches, St Anthony's Shrine, are frequented by foreign tourists, and Sri Lanka's foreign ministry said the bodies of at least 27 foreigners from a variety of countries were recovered. These included British, US, Turkish, Indian, Chinese, Danish, Dutch and Portuguese nations.

There were no immediate claims of responsibility for the attacks in a country which was at war for decades with Tamil separatists until 2009 during which bomb blasts in the capital were common.

Prime Minister Ranil Wickremesinghe called a national security council meeting at his home for later in the day.

"I strongly condemn the cowardly attacks on our people today. I call upon all Sri Lankans during this tragic time to remain united and strong," he said in a Tweet.

"Please avoid propagating unverified reports and speculation. The government is taking immediate steps to contain this situation."

President Maithripala Sirisena said he had ordered the police special task force and military to investigate who was behind the attacks and their agenda.

The military had been deployed, according to a military spokesman, and security stepped up at Colombo's international airport.

Chinese state media report that a Chinese citizen has died in the Sri Lanka attacks, while four Chinese nationals were hospitalised.

Portugal's Ministry of Foreign Affairs also confirmed that one victim was a Portuguese citizen.

One Dutch person was also among those killed in the bomb attacks, Dutch foreign minister Stef Blok said.

The US said "several" American were among the dead while Britain and China said they, too, lost citizens.

Christian groups say they have faced increasing intimidation from some extremist Buddhist monks in recent years.

And last year, there were clashes between the majority Sinhalese Buddhist community and minority Muslims, with some hardline Buddhist groups accusing Muslims of forcing people to convert to Islam.

Out of Sri Lanka's total population of around 22 million, 70 per cent are Buddhist, 12.6 per cent Hindu, 9.7 per cent Muslim and 7.6 per cent Christian, according to the country's 2012 census.

The scale of the bloodshed recalled the worst days of Sri Lanka's 26-year civil war, in which the Tamil Tigers, a rebel group from the ethnic Tamil minority, sought independence from the Buddhist-majority country.

During the war, the Tigers and other rebels carried out a multitude of bombings. The Tamils are Hindu, Muslim and Christian.

The heads of major governments around the world condemned the attacks.

US President Donald Trump offered condolences to the people of Sri Lanka and said the US stood "ready to help."

UK Prime Minister Theresa May called the attacks "appalling".

United Nations secretary general António Guterres said he was “outraged by the terrorist attacks” and stressed the “sanctity of all places of worship”.