one blast caused fuel tanks to explode others were a chain reaction...and yes in war when port is attacked then normal operations are suspended its not a new strategy invented by Indians....how was Karachi burning?
Karachi was your only port, half your fuel reserves were wiped out in Indian navy raids.
After the first attack on Dec 4, Karachi harbor burned for 4 days, the fires has just been brought under control, when the second attack happened and Kemari oil storage facility was burning for another 3 days.
Not the entire Karchi city, but part of the city, which was essential for your war effort, had been decimated.