He said there was a possibility the bodies had washed back onto the rock.
There will also be inflatable rescue boats, airforce Iroquois and a rescue helicopter helping in the search.
The police search team will focus their search around Omata, south of New Plymouth, which was where currents could have pulled them.
Mr Grant said the continued rough conditions meant it was unlikely divers would be able to search for the trio.
There was a candlelit vigil for the missing boys and instructor last night.
The students and Mr Jourdain were part of a group of 11 students from Spotswood College and another instructor from the Taranaki Outdoor Pursuit Education Centre.
Mr Grant said officials at Topec could be interviewed as part of a police investigation into the incident.
Spotswood College board of trustees chairman Ross Dingle said the school's focus was on supporting its students and the families of the missing.
Joao De Melo's father, Celio Fernando, told local media his son was an athlete who played many sports.
He still hoped his son had swum to safety and was waiting to be rescued.
The De Melo family, who live in Ceara in northeastern Brazil, was told of the incident on Wednesday afternoon and was in contact with Brazilian authorities in New Zealand.
Prime Minister John Key said a full coroner's inquiry would be held.
"We need to understand if there's been any errors ... and we'll get to the bottom of that.
"Any kind of physical activity like this comes with a degree of risk. But obviously we make sure, when youngsters are involved, that that's a very managed risk.
"If something's gone terribly wrong, which in this case it has, we need to find out why and if there's things that need to change, then they will be changed."
