"It's a pretty bleak outlook unfortunately."
The man's next of kin had been notified but police would not release his name until they were sure everyone who had needed to be contacted had been, Mr Borrell said.
West Coast police search and rescue co-ordinator Sergeant Sean Judd said a five-member whitewater rescue team, a helicopter and jetboats searched for the man yesterday.
Ground-based searches had been hampered by difficult terrain throughout the day.
Mr Judd said it appeared the man met up with a group of four-wheel drivers, but his association with them appeared sketchy.
Of the other four-wheel drivers at the river this morning, none spoken to by police so far knew the missing man. "There's a big gap and some of the people we're talking to now, they've just met up," Mr Judd said.
Yesterday distraught companions of a man washed away while four-wheel-driving raced across rough terrain for an hour to raise the alarm.
The missing man had been travelling with a group from Christchurch's 4X4 Events.
After the incident two people rushed to the home of Blair Webb to call for help.
"They were visibly upset. They said 'Somebody's gone into the river'," Webb said.
The pair, who arrived about noon, did not identify themselves or the missing man.
"Hopefully the dude is alright, and he's just washed up on a bank somewhere."
Webb's neighbour Alex Wingham said the area was popular with off-roaders.
"Every long weekend they come over from Christchurch. They cross the rivers and go up to Waipuna Station."
Ground-based searches had been hampered by difficult terrain throughout the day but the river would continue to be scoured while daylight remained.
"We're still looking. It's a remote area and information has been a little bit slow coming forth," Mr Judd said.
Ikamatua Volunteer Fire Brigade chief fire officer Nick Pupich said his firefighters spent several hours checking about four kilometres of river banks, before being pulled out late afternoon.
He described the river as being "fresh", rather than in flood.
A white water rescue team of five kayaks were also on the river yesterday searching for the man.
Police said wet weather was causing the river to run high and ground searches were hampered by the difficult terrain.
- Greymouth Star, Herald on Sunday