Government officials were working closely with the nation's poultry industry Friday to contain the worst outbreak of bird flu on record, one that already has prompted the governors of four states to declare emergencies and led to the culling of 33 million birds in 16 states.

Nebraska became the latest state to declare an emergency amid the outbreak, which has seen three deadly strains of avian influenza have hit North America since December. That action by Gov. Pete Ricketts followed similar moves in Wisconsin, Minnesota and Iowa. With the spread of infection picking up speed in recent weeks, the battle to stem the crisis has become an all-hands-on-deck situation.

"What makes this different is the size — so many hens have to be disposed of at once.”

- David Stecher, an organic waste management consultant

Earlier this month, Washington approved $330 million in emergency funds to help states fight the spread of bird flu with stepped-up biosecurity measures that include stepped-up monitoring and euthanizing millions of chickens.

In Iowa, where the state is sending mobile incinerators from farm to farm to destroy chickens, there are so many chickens to be killed that it is causing logistical problems. Poultry farms regularly cull older hens, but not in the numbers dictated by the current outbreak.

“There’s already a lot of infrastructure for depopulation in place in the industry,” David Stecher, an organic waste management consultant, told The New York Times. "What makes this different is the size — so many hens have to be disposed of at once.”

The $6 billion-per-year poultry exporting industry has been hit hard by international bans on U.S. supplies, including those imposed by China and Mexico.

Ricketts acted Thursday after federal agriculture officials confirmed a second farm site had tested positive for the rapidly spreading avian flu virus. The declaration opens the door to releasing emergency funds and other aid to the Nebraska Department of Agriculture and other state agencies trying to contain the bird flu outbreak.

The second case in Dixon County - a farm with 1.8 million egg-laying hens - is physically close to the first farm that tested positive earlier this week and is owned by the same company, state officials said.

"Having a second farm in Nebraska confirmed to have HPAI (highly pathogenic avian influenza) is unfortunate but not completely unexpected," said Nebraska Department of Agriculture Director Greg Ibach. "This follows the pattern we’ve seen in other states when it comes to the spread of the virus."

Although the U.S. poultry and egg industry is reeling, the current outbreak involves strains of bird flu that pose a low risk to human health, experts say. No human infections have been identified so far.

The main effect on humans is the soaring prices of poultry and eggs  the outbreak has caused. The cost of a carton of large eggs in the Midwest has jumped nearly 17 percent to $1.39 a dozen from $1.19 since mid-April when the virus began appearing in Iowa's chicken flocks and farmers culled their flocks to contain any spread. An even bigger increase has emerged in the eggs used as ingredients in processed products such as cake mix and mayonnaise, which account for the majority of what Iowa produces. Those eggs have jumped 63 percent to $1.03 a dozen from 63 cents in the last three weeks. Turkey prices, which had been expected to fall this year, are up slightly as the bird flu claimed about 5.6 million turkeys nationwide so far. 

The spread of the highly contagious H5 virus is worrying to farmers and investigators, who have hoped that warmer spring weather would help lower the number of infections in birds and curtail the virus' spread.

"Unfortunately, as many poultry farms are discovering, even our extraordinary measures proved ineffective in preventing the spread of avian influenza into one of our barns," Scott Ramsdell, of South Dakota-based poultry industry group Dakota Layers said.

On Monday, a strain of avian flu that had previously been found only in the Western United States cropped up in an Indiana backyard poultry flock, and officials warn it shows few signs of waning so far.

According to the Maryland Department of Agriculture, officials working to prevent the flu from spreading to their state have stepped up informational outreach to both commercial and backyard farmers who own poultry. Literature and posters have been distributed to homes, farms, and feed stores. At any given time, there are approximately 110 million chickens in Maryland, Delaware and Virginia.

“The big message is to increase and enhance biosecurity measures,” Maryland Department of Agriculture public information officer Vanessa Orlando told FoxNews.com. “The best we can try to do is keep it of houses— washing hands, tires, truck, feet, shoes.”

The state has been in conversations with other state emergency teams, as well as the National Emergency Management Association (NEMA) to prepare if the state were to get the fast-spreading disease.

All non-essential inspections of poultry have been suspended in Maryland to avoid potential, unintentional spread of the disease from farm to farm. 

“We’re preparing for it to come, hoping it doesn’t but trying to get prepared,” Orlando said. “We’re taking this very seriously.”

In Ohio, the state’s agriculture department has declared that poultry from states where the bird flu has been confirmed will not be permitted at this year’s Ohio State Fair as they ramp up efforts to prevent it from spreading to their state.

The Columbus Dispatch reports the state’s agriculture department also warns the fair’s poultry show may be canceled altogether if the outbreak gets worse.

Ohio Department of Agriculture spokeswoman Erica Hawkins says the fair’s situation is evolving and agriculture officials are focused on preventing the flu from coming to Ohio. The state is encouraging all county and independent fairs to also prohibit poultry entries from states with the avian flu.

The U.S. Department of Agriculture (USDA) is encouraging farmers to wear protective gear and respirators when depopulating poultry due to the unpredictable nature of the avian flu, said Dr. T.J. Myers, associate deputy administrator for veterinary services with the USDA.

“Our advice from our colleagues in the human health community is that they have not seen any evidence that this virus has any predilection in infecting humans, but even though that’s true, we are still taking precautions,” Myers told FoxNews.com. “There’s always a concern about any influenza virus continuing to mutate or change, and become a risk.”

The Associated Press and Reuters contributed to this report.