Two women were among the dead at a Methodist church in the restive southwestern city of Quetta in Balochistan province, said provincial police chief Moazzam Jah, adding that five of the injured were in serious condition.
Oficials said police intercepted and shot one bomber outside but the second attacker managed to reach the church's main door where he blew himself up.
"Police were quick to react and stop the attackers from entering into the main hall," Jah told AFP.
Balochistan provincial home minister Sarfraz Bugti said around 250 people normally attend the church on Sundays, but attendance had swelled to around 400 because it was close to Christmas.
"God forbid, if the terrorists had succeeded in their plans more than 400 precious lives would have been at stake," tweeted the home minister.
TV footage showed shattered pews and broken musical instruments littered across blood-smeared floors.
Christians make up an estimated 1.6 percent of Pakistan's 200 million people and have long faced discrimination -- sidelined into lowly paid jobs and sometimes the target of trumped-up blasphemy charges.
Along with other religious minorities, the community has also been hit by Islamic militants over the years.
In 2016 Lahore suffered one of Pakistan's deadliest attacks during the Easter season -- a suicide bomb in a park that killed more than 70 people including many children.
The bombing was later claimed by the Jamaat ul Ahrar faction of the Pakistani Taliban.
Police and troops have been battling Islamist and nationalist insurgencies in mineral-rich Balochistan for over a decade.
Balochistan, bordering Iran and Afghanistan, is the largest of the country's four provinces but its roughly seven million inhabitants have long argued they do not get a fair share of its vast gas and mineral wealth.
Efforts to promote peace and development have reduced the violence considerably in recent years.
The push includes ongoing work on a mammoth Chinese infrastructure project -- the China-Pakistan Economic Corridor -- which will provide Beijing with a modern-day Silk Road to the Arabian Sea through Balochistan's deep-sea port of Gwadar.
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