"We don't know what's happened - the cause of the fire is still unknown. We don't know what we can and can't do at this stage.
"When we know more we'll be able to go back inside and start rebuilding."
Mr Brown posted a photo of the restaurants' kitchen on Facebook yesterday which appeared to show wires hanging from an exposed ceiling with insulation, dust and other debris throughout the area.
He said his staff were all "a bit shellshocked" today.
"We're absolutely gutted. It's a very sad day but the big thing is no one was hurt. Everyone in the SkyCity vicinity is like family. Everyone's been very supportive."
Mr Brown said Depot was in better shape than Federal Delicatessen and would likely open sooner. "People will be able to have the food they love again soon. When we reopen we'll be better than before."
Neighbouring restaurant Masu was evacuated yesterday but operated as normal last night and was open today.
More than 200 Sky City staff were also evacuated from Federal House, where smoke could be seen from the top of the building. There was no damage to the building and staff returned to work promptly.
The casino and hotel weren't evacuated.
A SkyCity spokeswoman said this morning it would be assessing what had happened.
Twelve fire trucks and about 50 firefighters battled yesterday's blaze.
Fire Service spokesman Dave Carroll said yesterday the fire was believed to have started in chimney ductings.
"There is a large amount of ducting chimneys and they go through the kitchens in all these restaurants and things," Mr Carroll said.
"The smoke as fumes get sucked out, and one of the ductings has caught fire around the back."
Depot Eatery & Oyster Bar is expected to reopen next week.
Sky City chief operating officer John Mortensen said the restaurant's damage wasn't as bad as expected.
"The damage to Depot is not as bad as we thought and the kitchen is largely in one piece," he said.
"Unfortunately this is not the case for Federal Delicatessen which will be closed for some time."
Fire Service spokesman Dave Carroll confirmed this morning the fire started in chimney ducting in the kitchen's ceiling.
The 600ml round chimney ducting began at the top of the kitchen's woodfire pizza oven, went for about six metres through the kitchen and then bent and went up through the roof, he said.
"The heat from around the ducting caused the timbers to catch fire," Mr Carroll said. "Residue builds up in the corners of the ducting but it gets serviced regularly.
"In this case, it still managed to catch fire. We're not yet entirely sure why."
Mr Carroll said the building's structural damage wasn't significant. "There's a bit of damage to the roof of the kitchen but for the most part, everything in there probably just needs a good clean."
Fire engineers had been investigating the cause of the fire this morning and would release a report in the next couple of days, he said.
More than 100 staff were affected by the eateries' closure.
A spokeswoman for Al Brown said they were not able to comment on how much business had been lost at this stage but said both restaurants were insured.
It wasn't yet known when Federal St Deli would reopen.
The spokeswoman said they would have a better idea next week when it would be up and running again.
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