Its ammonia reserves - used to refrigerate the ship - were being pumped off the ship at the Stark Bros Ltd dry dock at Godley Quay all afternoon.
The gas leak hampered any investigation in the fire's cause, said fire safety officer Graham Davies.
"The ammonia leak has meant we've been pretty limited as to what we can do and where we can go," he said.
"We've been talking to the companies working on the boat, to find out what they were doing, and where they were working,
"The actual physical part of the investigation will likely take place tomorrow and I'd hope that by the end of tomorrow we should have a pretty good idea of the cause."
Representatives of the ship's owners were due to go aboard today to survey the extent of the damage and the ammonia leak.
No one was on board the vessel before the fire started at around 5.30pm yesterday.
Environment Canterbury (Ecan) has been notified of the leak and a spokeswoman confirmed a compliance officer had been sent to the scene to check for any "potentially contaminated water".
Meanwhile, it was business as usual for the rest of Lyttelton Port.
Lyttelton Tunnel was initially closed last night to all but emergency vehicles, but is now open.
Amateur photographer Aaron Campbell raced over to Lyttelton from his Christchurch home when he heard of the blaze last night.
He arrived within around an hour of its outbreak, and captured the most striking images of the event.
Mr Campbell said local residents reported "a bang - or several bangs" and thought it was fireworks.
