Church bells tolled at Colombo's devastated St Anthony's Shrine, as people wept, prayed and lit candles for the victims of the horrific bomb attacks last Sunday.

The bells rang out at 8.45am, the moment a jihadist suicide bomber detonated his device inside the 18th-century church on Easter Sunday, one of six attacks on churches and luxury hotels that left 253 dead.

The bomber destroyed part of the shrine's roof and scarred its walls with shrapnel, damaging the clock tower whose hands were still stuck at 8.45, a grim reminder of the destruction wreaked.

Sri Lanka’s Catholic hierarchy has cancelled all public services, fearing new attacks.

But this morning, scores of Catholics held a heavily guarded vigil outside the Colombo church.

From teenagers to elderly men and women, to parents carrying their children in their arms, the crowd gradually swelled, as worshippers came out on to the streets to mourn.

Keuslaus Stanislaus said he had travelled to St Anthony's because he "wanted to participate in a mass in some way".

"We wanted to participate because we haven't been able to worship all week," he said.

For those living near the church, the bombing felt like a personal onslaught.

"I come to this church every Sunday. It feels like my second home. It's like people blasted my own home," said Dharshika Fernando, struggling to hold back tears.

"We don't know when the church will open again but we want it back soon," the 19-year-old said.

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About an hour after the vigil began, worshippers fell silent as the parish priest walked out to the entrance of the church and held up a statue of St Anthony.

The crowd raised their hands in prayer before resuming their solemn hymns.

At the tightly-guarded Archbishop's residence in Colombo, Cardinal Malcolm Ranjith condemned the attacks as "an insult to humanity", in a private mass that was broadcast live on the country's television channels.

With President Maithripala Sirisena, Prime Minister Ranil Wickremesinghe and opposition leader Mahinda Rajapakse in the small congregation, the cardinal appealed for peace and unity in the multi-ethnic island of 21 million people.

"In the name of God we cannot destroy any person," he said.

"What happened last Sunday is a great tragedy, an insult to humanity," the cardinal said, urging followers to show kindness to others as a sign of respect for all the victims.

The authorities have blamed the attacks on a local Islamist group affiliated to the so-called Islamic State, which has claimed responsibility.