Parts of the centre remained cordoned off on Sunday
Rob Watson, from Cambridge, was in a taxi on the way to the Zanzibar nightclub, near where the bomb went off, when he heard a loud bang.
The 23-year-old web designer got out of the taxi to see what it was and saw smoke coming from the back of a car parked in Smallbrook Queensway.
He told BBC News Online: "I thought it was a bomb as soon as I heard the bang because it was too loud to be a firework.
'Anthrax concern'
"I got out of the taxi and walked down to the road - it was before it had been cordoned off - and I saw a car still smoking. The windscreen of the car behind it had been blown out.
"There was quite a lot of dust and white powder about the place and at first I was very concerned because I thought it may have been anthrax.
"There were a few people about but they seemed to be quite calm because they had had a few drinks."
He added: "We managed to go into Zanzibar for half an hour before we all got evicted and then there were a lot of people on the street.
"They were more concerned than panicking.
"This hasn't put me off going into Birmingham because there is always a chance that things like this are going to happen."
Clubs evacuated
Thousands of people were evacuated from pubs and clubs in the area.
Guests at the Ibis hotel near New Street station were also told to leave the premises.
A clubber, who was in a nearby nightclub at the time the bomb went off, said he has been stranded in Birmingham after leaving his car in a street which has now been cordoned off by the police.
He said: "I heard something and came out to see what it was.
"My car was parked on double yellow lines but police have told me I can't get to it so I am still here, stranded in Birmingham."
On Sunday, Birmingham City Council leader Albert Bore said the council would be working closely with the police to ensure the city remained a "safe and peaceful" place.
He said: "I am relieved that nobody was killed or injured in last night's bomb blast.
Business as usual
"Birmingham people have memories of the tragic 1974 pub bombings and those of us in the city are determined that this latest incident will not deflect from sealing a peaceful end to the troubles in Northern Ireland.
"We will continue to work closely with the police to keep the city peaceful and safe for everyone who lives, works or visits Birmingham."
The bomb blast came on the eve of the annual Confederation of British Industry (CBI) meeting in Birmingham.
Director-general Digby Jones said it was business as usual.
"One of the great things about holding conferences in Birmingham is that it's a very secure city and has great experience.
"When it comes to conferences this is not something new for Birmingham .
"I couldn't think of a better place from a security point of view if you are holding a conference with a lot of important people attending."
On Sunday afternoon, parts of the city centre were still sealed off to the public while investigations continued.
New Street station remained open and rail services were not affected although access for passengers was restricted to one entrance in Navigation Street.