Shortly after those blasts were reported, police confirmed three hotels in the capital had also been hit, along with a church in the town of Batticalao, in the east of the country.
Photos circulating on social media showed the roof of one church had been almost blown off in the blast.
The floor was littered with a mixture of roof tiles, splintered wood and blood.
Several people could be seen covered in blood, with some trying to help those with more serious injuries.
Only around six percent of mainly Buddhist Sri Lanka is Catholic, but the religion is seen as a unifying force because it includes people from both the Tamil and majority Sinhalese ethnic groups.
St Anthony's Shrine and the three hotels where the blasts took place are in Colombo, and are frequented by foreign tourists.
The British High Commissioner to Sri Lanka has condemned 'evil attacks'.
James Dauris said he was in Colombo with his family at a church service which was cut short by the attacks.
He tweeted: 'Our prayers for the victims of these evil attacks, and for their families. Our thoughts are with the medical staff, police and all involved in the response.'
Shadow education secretary Angela Rayner wrote: 'Shocked and saddened by news of church and hotel bombings in Sri Lanka. Profound condolences to those who suffered in this terrorist attack, another attack on innocent people, truly awful news.'
Her Labour colleague Mary Creagh posted on Twitter: 'Sickening #EasterSunday #SriLanka terrorist attacks on churches & hotels. Terrible to target Christians celebrating our greatest feast day. My prayers are with victims, their families & everyone caught up in this cruel violence.'
Jess Phillips, MP for Birmingham Yardley, wrote: 'To target Christians on this their most sacred day is evil. Sending love to Sri Lankans caught in this terror.'
Brexit minister James Cleverly wrote: 'Sad and shocking news from Sri Lanka. My thoughts are with the Sri Lankan community both here in the UK and around the world and to those who have lost friends or family in these terrible attacks.'
A spokesman for the Foreign and Commonwealth Office said: 'We are aware of reports of a number of explosions in Sri Lanka, including Colombo, and we are urgently seeking information from the local authorities.
'British nationals in Sri Lanka should follow the instructions of the local authorities and check FCO travel advice for updates.'
Prime Minister of Pakistan Imran Khan wrote: 'Strongly condemn the horrific terrorist attack in Sri Lanka on Easter Sunday resulting in precious lives lost & hundreds injured.
'My profound condolences go to our Sri Lankan brethren. Pakistan stands in complete solidarity with Sri Lanka in their hour of grief.'
Prime Minister of India Chowkidar Narendra Modi said: 'Strongly condemn the horrific blasts in Sri Lanka. There is no place for such barbarism in our region. India stands in solidarity with the people of Sri Lanka.
'My thoughts are with the bereaved families and prayers with the injured.'
Blasts come amid rising religious tension between Buddhists, Muslims and Christians
The Easter Sunday attacks on churches and hotels in Sri Lanka are the latest flashpoint amid ongoing religious tensions in the island nation.
Sri Lanka has long been divided between the majority Sinhalese, who are overwhelmingly Buddhist, and minority Tamils who are Hindu, Muslim and Christian.
The country remains deeply scarred by its 1983-2009 civil war, when Tamil rebels fought to create an independent homeland.
The rebels were eventually crushed but a religious divide has taken hold in recent years.
A Christian group said there had been 86 cases of discrimination, threats and violence against followers of Jesus last year, with another 26 so far this year.
The U.S. State Department warned in a 2018 report that Christians had been pressured to close places of worship after they were deemed 'unauthorised gatherings'.
The report also said Buddhist monks regularly tried to close down Christian and Muslim places of worship.
There have also been attacks on Muslims, with the government forced to declare a state of emergency amid a spate of anti-Muslim rioting.
Hard-line Buddhist groups accuse Muslims of forcing people to convert and destroying sacred Buddhist sites.
One radical Muslim group, the NTJ, has been linked to the vandalisation of Buddhist statues and has also reportedly plotted to attack Christian churches.
Out of Sri Lanka's total population of around 22million, 70 percent are Buddhist, 13 per cent Hindu, 10 per cent Muslim, and seven per cent Christian, according to the country's 2012 census.