At least 67 South Africans were killed when a church hostel belonging to Nigerian TV evangelist TB Joshua collapsed in Lagos last week, South Africa's President Jacob Zuma has said.
Nigerian rescue workers now say at least 70 bodies have been pulled from the rubble.
It is the deadliest incident involving South Africans abroad "in our recent history", Mr Zuma said.
Mr Joshua, one of Nigeria's best-known evangelists, is popular across Africa.
Nigerian authorities are often reluctant to release death tolls.
The multi-story building served as a guesthouse on the campus of the televangelist's Synagogue, Church of All Nations.
- Founded Synagogue, Church of All Nations in the 1990s
- Runs Christian television station Emmanuel TV
- The ministry professes to heal all manner of illnesses
- Controversially this includes HIV/Aids
- Known as the "Prophet" by his followers
- Tours Africa, the US, the UK and South America
It was housing visitors from elsewhere in Nigeria and other countries.
Mr Joshua had said a small plane had been circling over the building before it collapsed on Friday afternoon, and suggested it was an attempt on his life.
On Tuesday, however, a rescue official said the likeliest cause of the building's collapse was the construction of additional storeys without reinforcing the foundations.
'Hostile to rescuers'
At least 130 people, including many foreigners, were pulled out of the rubble.
Officials says members of the church at first prevented emergency workers from participating in the rescue.
"For the first three days of the incident, the church people were very hostile and prevented rescue officials' access to the site," a spokesman for Nigeria's National Emergency Management Authority (Nema), Ibrahim Farinloyeh, told the AFP news agency.
BBC's Pumza Fihlani in Johannesburg:
OR Tambo International Airport in Johannesburg is crowded with people awaiting the return of their loved ones from Nigeria. So far one plane has returned.
It is understood that about 300 people, not all South African, travelled from South Africa last week to Lagos for one of Mr Joshua's healing gatherings.
The lack of information from Nigeria has not helped anxious relatives. The South African government has now set up a phone number for people to call for assistance, because some had been contacting the Pretoria embassy and phoning into local radio stations with the names of family members who had travelled to Nigeria.
Charismatic churches are hugely popular in South Africa, with Nigerian Pentecostals striking a particular chord. Thousands of TB Joshua's followers wait in queues, sometimes overnight, to catch a glimpse of the "Prophet" when he visits. He packs out stadiums on his tours.
It is believed that at least five South African church tour groups were visiting the church at the time of the collapse.
"This is a particularly difficult time for South Africa. Not in the recent history of our country have we had this large number of our people die in one incident outside the country," Mr Zuma said in a statement.
"Our thoughts are with the families, friends and colleagues that have lost their loved ones in this heart-breaking tragedy. The whole nation shares the pain of the mothers, fathers, daughters and sons who have lost their loved ones. We are all in grief."
Following the collapse, Mr Joshua has continued to post scriptures on social networking sites to his hundreds of thousands of followers.
Known as the "Prophet", he regularly preaches to large crowds at a mega-church in Lagos's Ikotun district.
His followers in Nigeria and abroad believe he has the gifts of healing and prophecy.