Most people mistook the blasts for something else - before rushing to a safe refuge and later helping the injured.
"I was in office when there was suddenly a loud noise. Initially we thought that a building had collapsed and we all ran out," said Akshay Shetty, an office goer near Opera House in south Mumbai where one of the three blasts took place.
"When we came out, there was a lot of smoke and we saw injured people lying around. Only then did it dawn upon us that it was a blast and we rushed to help the victims," he added.
Added Jayash Mehta, another eye witness: "I thought it was a cylinder explosion. It's shocking...I can't believe we have become the victims of a terror strike yet again".
Three explosions went off within minutes of each other here on Wednesday evening, leaving at least 21 people dead and 141 injured and sparking minor fires, in the first terror attack in Mumbai after November 2008.
The fires were quickly put out, and police quickly moved into all three areas - Dadar in central Mumbai and Opera House and Zaveri Bazar in south Mumbai.
All three are busy commercial and residential areas, and were bustling with people and traffic during the evening peak hours when the explosions took place.
Vikas Bajaj, a Dadar resident tweeted that he was so terrified that he couldn't move.
"I was terrified. I couldn't move," Bajaj said.
At Zaveri Bazaar, Shobhika Jain, eye witness said: "I was on my way back from work when I heard a loud noise....I was left shell shocked. Only when I saw people rushing around I came back to life and rushed to take refuge."
"I can't believe this is happenning to us, to my city again," she sobbed.