Emperor breaks his silence as stark warnings prompt nuclear panic

Japanese riot police have joined the desperate fight to stop a badly damaged nuclear plant from going into meltdown, bringing in a water canon truck to cool an overheating reactor. Their deployment last night heightened fears that the plant operator, Tokyo Electric Power (Tepco), is quickly running out of options.

Fears intensified last night when Greg Jaczko, chairman of the US Nuclear Regulatory Commission (NRC), said attempts to cool reactors to prevent meltdown appeared to be failing, adding that that one reactor was out of coolant, a claim denied by the Japanese authorities. The US Energy Secretary Steven Chu told members of Congress that the situation is "very significant, perhaps beyond Three Mile [Island]".

Technicians at the Fukushima Daiichi nuclear plant who had been using seawater and helicopters to dump water on the crippled facility were pulled out yesterday for over an hour after radioactivity levels spiked. Tepco later sent more than 100 men in protective suits back inside.

Reactor 3 has reportedly been leaking radiation since an explosion damaged its containment system and Tepco has refused to rule out the threat of "criticality" – a potentially catastrophic fission explosion in Reactor 4. The riot police will try to bring the situation under control by spraying pressurised water into a storage pool for spent nuclear fuel inside No 4 reactor.

The depth of the crisis was underlined yesterday in a rare TV appearance by Emperor Akihito, who said he was "deeply concerned" by the tragedy enveloping his country. "I hope from the bottom of my heart that the people will, hand in hand, treat each other with compassion and overcome these difficult times," he said.

The first statement of its kind by the emperor brought back memories of the Second World War and of the 1995 Hanshin earthquake, which killed 6,000 people in and around Kobe. Rumours had been spreading in Tokyo that the Emperor had left the city for Kyoto after low-level radioactivity spread throughout the capital.

Five nuclear workers have reportedly died since the quake and tsunami hit on Friday, knocking out diesel-fuelled cooling systems. Two more are missing with at least 20 injured. The unheralded technicians, who are virtually the only firewall in the nuclear crisis, were put at further risk on Tuesday when the health ministry more than doubled their radiation-exposure limit to 250 millisieverts.

A US watchdog is warning that the crisis at Fukushima could reach the "worst level on an international scale of zero to seven". The Institute for Science and International Security (Isis) called the situation "closer to a level 6, and it may unfortunately reach a level 7". It rated the 1986 Chernobyl disaster at seven and the 1979 Three Mile Island incident at five.

The government's top spokesman, Yukio Edano, continued to insist yesterday that contamination was comparatively low, even within the 20km radius of the Fukushima complex.

"If someone were to stay in the area for 24 hours a day, 365 days a year, they might suffer health problems. But the radiation is not high enough to affect the human body over several hours or even days."

With radiation around Tokyo still higher than normal and the danger of a major disaster unfolding just 250km away, foreign embassies have been advising nationals to leave. The UK joined the group last night as France sent two planes to evacuate its citizens. The embassies of Iraq, Bahrain and Angola say they will close. Panama and Austria have also evacuated their ambassadors to Kyoto. Japan's foreign ministry criticised the warnings last night, urging calm and asking foreign diplomats and government officials to "accurately convey" information about Fukushima. Some commentators have accused the foreign community of overreacting.

There were signs yesterday, however, that Japanese people are also increasingly heading for train stations and airports. At Shinagawa Station, a main Tokyo transport hub, hundreds of women with children bought tickets for the Shinkansen bullet train.

"I'm going home to my mum's place in Kansai," said Akina Suda, 25, clutching her three-month-old infant. "I saw old television footage of what happened to children in Hiroshima and Nagasaki. Radiation is very dangerous for babies and I want to protect mine."

Yuko Kasamatsu held her two-year-old daughter, Rio, as she prepared to board a train west. "I'm going back to my hometown, Kyoto," she said. "There is an awful lot of unreliable information on the Web so I stuck to official sources about the radiation. I don't think it's very dangerous now, but if anything happens it will be too late to get out, so I'm taking no chances."

British national Simeon Allan with his wife Mari and daughter Akari, said: "My wife is taking our child to Kansai. If the situation worsens, I may join her."

The Fukushima crisis has overshadowed the plight of about 450,000 refugees, mainly in the decimated north-east of the country. The government said yesterday that the death toll had climbed to 3,700 but thousands more are missing.

Japanese TV channels turned last night to two miracle stories amid the disaster. In the coastal town of Ishinomaki, in hard-hit Miyagi Prefecture, soldiers pulled a four-month-old baby alive from the wreckage – she was swept out of her parents' arms when the tsunami hit. And a woman from the town of Minami-Sanriku, which lost over half its population, gave birth to a healthy son.

"Is it OK for me to be so happy when so many are suffering?" the mother, Yukie Kanno, said on Japanese TV.