The health threat posed by the continuing nuclear catastrophe in Japan is starting to look less like Three Mile Island and more like Chernobyl.
As the earthquake-induced disaster worsens, the government has confirmed that radiation levels in the vicinity of the Fukushima Daiichi plant are now dangerous to human health.
More than 70,000 people have already been evacuated from within 20 kilometres of the stricken facility, and 140,000 people living within a 30-kilometre radius have been warned by the government to remain inside.
"Please do not go outside. Please stay indoors. Please close windows and make your homes airtight," was the message issued by chief cabinet secretary Yukio Edano. "These are figures that potentially affect health. There is no mistake about that."
Levels of 400 millisieverts an hour were recorded near the plant's reactors and radiation levels of up to 100 times the normal amount have been detected in the neighbouring prefecture of Ibaraki. Exposure to more than 100 millisieverts a year can lead to cancer, while short-term exposure to about 10,000 millisieverts would cause immediate illness, nausea and decreased white blood cell count, and could cause death within a few weeks.
In Tokyo, officials endeavoured to persuade residents that a slight increase in radiation levels was too small to threaten the city's population of 39 million.
"The amount is extremely small, and it does not raise health concerns. It will not affect us," said Takayuki Fujiki, a Tokyo government official.
But the threat of radiation poisoning has seen panic ripple across the country and beyond.
Some international embassies have relocated out of the capital, or evacuated their staff entirely.
Stores shelves are empty as people stockpile goods and retreat to the relative safety of their homes - if their homes are still standing in the areas that were hit hard by last week's 9.0-magnitude earthquake and tsunami.
Rick Holt, the Industrial Research Chair of Nuclear Materials at Queen's University, said that staying inside is just a short-term solution.
"If there's radioactivity blowing by outside, you'll be protected if you're indoors," he said. "If it gets to the point where that's not good enough, you have to evacuate."
In the long term, he said that those close to the radiation clouds "should get far away from it."
But with damaged roads and devastated homes, the threat of a mass exodus could create further problems for the suffering nation, with millions of citizens potentially seeking out safer ground away from the nuclear site.
Already, the government is doing its best to stem the spread of panic and play down the health risks of the nuclear situation.
News that people in the area around the plant are being given potassium iodide pills has caused a global rush for the medication, which can help prevent thyroid cancer after radiation exposure by reducing the amount of radioactive material absorbed by the gland.
The World Health Organization turned to the social messaging site Twitter to warn against the rush, releasing the statement: "Consult your #doctor before taking #iodine pills. Do not self-medicate!"
There has even been a run on the pills in British Columbia, prompting the province's top medical officer, Perry Kendall, to release a statement asking pharmacies not to sell them.
"The consumption of iodide tablets is not a necessary precaution as there is no current risk," he wrote. "Even if radiation from Japan ever made it to British Columbia, our prediction, based on current information, is that it would not pose any significant health risk."
In the Philippines, there was widespread panic after a hoax text message purporting to be a BBC news flash claimed that radiation had reached the island nation. Both the BBC and the Philippines government refuted the rumour, but that did not stop some schools from closing and offices from sending workers home.
In Japan, citizens across the country expressed concern about potential exposure to radiation and tourists rushed to get home.
"I worry a lot about fallout," said Yuta Tadano, a 20-year-old pump technician at the Fukushima plant, who was in the complex when the quake hit. "If we could see it, we could escape, but we can't."
At the site itself, 70 plant employees are reportedly still at work trying to contain the disaster.
Another 800 staff were evacuated and explosions at the reactors have injured 15 workers and military personnel and exposed up to 190 people to elevated radiation.
After the nuclear disaster at Chernobyl, in the Ukraine in 1986, 130,000 residents were permanently resettled, 31 employees died from radiation poisoning and another 238 suffered from acute radiation syndrome. There was also a marked increase in thyroid cancer among children in the affected area.
A more contained nuclear meltdown at Three Mile Island in 1979 prompted Pennsylvania's governor to evacuate children and pregnant women living within eight kilometres of the plant.