Emergency services said that 29 people were rushed to hospital after the collapse in the coastal province of KwaZulu-Natal.
Local officials have blamed the tragedy on heavy rainfall in the area around eMpangeni on Thursday night.
Most of the victims were reportedly women sleeping in the church.
An 11-year-old girl is thought to be among them.
The wall at the front of the Pentecostal Holiness Church collapsed at the start of what had been planned as a weekend-long service to commemorate the Christian festival of Easter.
On Friday, a special prayer service was held in a large tent in front of the church, reports the eNCA TV station.
The Reverend Thulasizwe Buthelezi, the mayor of Zululand municipality, said the community was devastated and they would be praying for those affected by the tragedy.
"Christians [from] all denominations - we are here in solidarity. We are here to pray with the church, to pray with the families and to offer our support that God may really heal their wounds."
President Cyril Ramaphosa visited the church last year and some of the congregants reportedly asked for his support to build a new church.
Labour Minister Mildred Oliphant is a member of the church and was planning to attend the Good Friday service there.
She visited the scene and said: "Even at this difficult time, we still need to trust in God."