Over the past 30 years, Bernd Domres has rushed to earthquakes from Armenia to Algeria to Haiti. The German doctor has struggled with horrendous roads, filthy hospitals and other familiar challenges of the developing world.

He’d take them all over hyper-modern Japan. “I’d rather be working with a pocketknife in Haiti than worrying about the danger of a radioactive cloud,” the 72-year-old surgeon said.

After an overnight flight from Munich, Domres and five other members of his German medical team arrived in Tokyo just as news broke of an explosion at a nuclear power plant in Fukushima, about 150 miles north of the capital and south of the quake-stricken city of Sendai.

Japan, bereft of oil and gas reserves, has developed an extensive nuclear power industry. The blast at the Fukushima Daiichi plant could signify the gravest nuclear power crisis since the 1986 Chernobyl disaster, which contributed to the collapse of the Soviet Union, although early fears of a meltdown appeared unfounded, at least for now.

Domres and his team, from the medical charity Humedica, had planned to leave Narita International Airport, east of Tokyo, immediately and drive due north to the areas hardest hit by Friday’s 8.9-magnitude quake, Japan’s worst on record. They had barely cleared the arrivals hall when they saw Japanese passengers and airport staff members gaping in dismay at a big television screen showing pictures of the smoking nuclear plant.

Yoshi Sato, whose family lives near the plant, said he was very worried. “Who knows what will happen now?” he said.

How much radioactive material may have leaked remained unclear late Saturday. Japanese authorities said the explosion had not ruptured the core nuclear container and intimated that a widespread leak could be avoided.

Still, fear rippled through Japan, a country with peerless know-how in dealing with quakes but a mixed record of nuclear safety, as it confronted a threat it couldn’t see.

Any risk to major population centers will rise or fall depending on the the weather. If winds blow from north to south, any radioactive cloud could end up in Tokyo.

Domres said that he, like nearly everyone here, was in the dark about exactly what had happened and that he wouldn’t be driving too far north until he finds out. “It is certainly not advisable right now,” he said.

If winds shift and serious leakage has occurred, he warned, “a cloud will approach this area loaded with radioactive material.” On Saturday, Japanese police sealed off major roads leading north, and trains were not running to the area.

Darren Livengood, an American who has been working in Tokyo for a decade, said he has experienced many tremors before but nothing like Friday’s. At work at the time in a Tokyo office building, he and his co-workers ran outside after a “couple of very violent shakes” made “very clear that this was far worse than usual.”

Fear of radiation added another layer of alarm Saturday as aftershocks continued. “It’s freaky,” he said. “Japan is extremely safety-conscious and would have cleared us out” if the risk of contamination were serious.

“Unless it is too late,” he added wryly.

Domres, the surgeon, said he had traveled to Haiti twice after the earthquake there in January 2010.

“That was not easy,” he said, because of robbers and appalling sanitary conditions. Japan, he said, is nothing like that: “It is very, very developed.”

Still, the doctor said, “I’d prefer to be in Haiti. There were no worries about radiation. You could get to the area.”

Early Sunday, the German medical team announced that it was aborting its plan to go to the quake zone and would leave Japan. Domres cited the restrictions Japanese authorities had imposed on travel to the area and fears that radiation levels are higher than the government has said.

“It is worse than we are being told,” he said.