The Rev. Nico Smith, a white pastor who challenged South Africa's apartheid system by moving with his wife into a black township in the 1980s, has died of a heart attack, one of his daughters said Sunday. He was 81.

Smith collapsed while attending a friend's birthday party Saturday in Pretoria, and died before he could be taken to a hospital, said Marita Laubscher, the eldest of his three daughters.

In the tumultuous '80s, Smith was one of a tiny handful of clerics who left the white Dutch Reformed Church — the largest denomination among the Afrikaners who then held political power — because of the church's refusal to actively oppose apartheid. Smith instead joined the denomination's black offspring....