East Riding of Yorkshire Council’s public health director Andy Kingdom said cases of the strain could be confirmed within as early as a week and it may already have arrived.
He added health officials were concerned because it appears to double case rates in two to three days rather than 24 days with Delta, risking the rapid overwhelming of hospitals.
The appeal comes as 1,459 coronavirus cases were recorded in the East Riding from Tuesday, November 30 to Monday, December 6, down from 1,487 the previous week.
The infection rate fell from 433 to 425 cases per 100,000 people during the same period, with the latter comparing to 501 for England and 359 for Yorkshire.
The number of coronavirus patients in Hull Royal Infirmary and Castle Hill Hospital was 81 at the latest count, compared to 48 at the start of November.
Mr Kingdom said the speed at which Omicron doubles its case numbers led to health officials recommending the move to the Government’s Plan B for coronavirus measures.
He added it was unknown whether the strain was more harmful or resistant to vaccines, calling on people to help buy time for the NHS to do more booster jabs.
The director said: “Before the arrival of Omicron we thought we’d seen the worst of the storm off, our numbers in older age groups were coming down, it was still raining but it was more like drizzle.
“Now the black cloud of Omicron is on the horizon, we’re looking very hard to find cases here and we’re testing some possible ones but there’s none confirmed in the East Riding yet.
“But it is coming our way, and it’s coming quickly.
“Viruses survive by copying themselves but the copies are never exact and the changes can either give them advantages or disadvantages in spreading.
“Omicron appears to have about 32 mutations which give it advantages, the main one we know about now is that you can catch it quicker.
“Before we were seeing the tail end of Delta and the pool of people coronavirus could infect was shrinking because people were jabbed or had some level of immunity.
“But Omicron has brought some people who were no longer at risk back into play.
“From what we can see from South Africa so far it doesn’t appear to be more harmful, but that country has a younger population who can deal with coronavirus better so we’ll have to wait and see if that’s the case generally.
“And the signs are that the booster should be effective against it, but whereas before we needed two jabs now we really need three.
“We’re in a much better place than we were last year because now we’ve got the vaccine.
“But Omicron means we’ve got to do more to make jabs and all the other measures work.
“As with before the East Riding is the last place on the map coronavirus tends to reach, the more time we can buy the better.
“So as with preparing for a storm, you need to have as many layers of protection as possible.
“The vaccine acted as the big winter coat, but with Omicron we’re not sure now if it’s entirely waterproof yet.
“So the measures announced this week are about adding extra layers, putting extra jumpers on underneath just to be sure, I’m hoping it won’t be as serious as we fear but we need to prepare.
“And the more we can do, including wearing masks and all enclosed or crowded public spaces not just those in the rules and those eligible getting boosters, the better position we’ll be in to face the storm.”