The anti-apartheid struggle icon was wearing his signature black and gold Madiba shirt. A glass dome covered his peaceful-looking face.
Overwhelmed by emotion, some people silently wept. A police officer tried to comfort a woman in apparent shock.
Correctional services officer Abigail Zuma said she got closure from seeing the body.
"I feel fulfilled but very emotional," she said as she held a colleague's hand for support.
"I saw him and I'm happy that he's resting peacefully."
Zuma said seeing Mandela made her death a reality.
"I feel I am part of history."
Another correctional services officer Norman Tshivhase, said it was a difficult moment for him.
"It was bad to see my leader, my real comrade, lying down like that.
"I got closure," said Tshivhase, wearing a red SA Communist Party cap and T-shirt.
Hundreds of people queued at the Union Buildings waiting to say their last goodbye to the "father of the nation".
Mandela will again be transported from One Military Hospital to the Union Buildings on Friday, where his body will lie in state for the third and last day.
Members of the public are invited to line the route and form a public guard of honour while his body is being transported.
People can view the body from 08:00 to 17:30.
Mandela died at his home in Houghton, Johannesburg, last Thursday, at the age of 95.
The official memorial service was held at the FNB Stadium, in Soweto, on Tuesday, and was attended by about 100 current and former heads of state and government.
He will be buried in Qunu in the Eastern Cape on Sunday.
