Relatives of the firefighters who perished while putting out a fire inside a Johannesburg building poured their hearts out on social media a day after the horrific incident.

Simphiwe Moropane, 28, Khathutshelo Muedi, 37, and Mduduzi Ndlovu, 40, lost their lives on Wednesday while on a mission to extinguish the flames that broke out on the 23rd floor of the Bank of Lisbon building shared by three provincial government departments.

On Thursday, Ury Ratseke, who claimed one of the firemen was her husband, took to social media to express her grief.

"Today I lost my husband, best friend, father to my children. I love you so much," Ratseke posted.

The post which grabbed the attention of thousands of social media users was accompanied by family pictures showing Ratseke with the deceased and their children.

In one of the images posted by Ratseke, the firefighter can be seen holding a baby while looking adoringly at his bundle of joy.

People were sending messages of support while also donating money towards a crowd-funding page - reaching R15637 by Wednesday afternoon.

In another picture, the couple can be seen looking lovingly into each other's eyes with the caption "he honestly had the most contagious smile in the world" written above it.

Ratseke's post was retweeted more than 7000 times with people describing the firefighter as a hero.

"Your husband was a soldier, a hard worker and a friend to many," commented Phindokuhle Maseko.

Israel Muedi also posted about his brother Muedi.

"My brother died a hero not just for the Rambau family but for the people of South Africa. More than 1500 government employees were rescued.

"A true firefighter is like a soldier, he died doing his best protecting his people."

His post was flooded with messages of condolences from friends and family.

"A hero indeed, we are proud of him," commented Ndidzu Masindi.

Livhuwa Nenghovela said: "He wasn't our neighbour but we grew up seeing him as our big brother.

"I am still in shock now but only God knows."

On Thursday, some of the affected relatives gathered at the Fairview fire station where they met City of Johannesburg mayor Herman Mashaba and Gauteng premier David Makhura.

Mashaba addressed members of the media after the meeting, saying that the families were grief stricken.