It is a disaster but the full extent is unknown. The question is not whether this qualifies as a disaster, it's a question of how big, how many people are effected and how long it will take to get under control. Only then can we start talking about remediation.
Already the authorities have reported radioactive contamination outside the reactors site, at the moment most attention is being focused on two radioactive elements: Iodine-129 and Caesium-137 contamination in particular.
Here is Time magazine on on iodine contamination:
When thyroid cells absorb too much radioactive iodine — either through the air or through contaminated food — it can increase the risk for thyroid cancer, says the American Thyroid Association. Babies and young children are at highest risk as their thyroid glands are most radiation-sensitive. People over 40 are at less risk.
Here is the US Environmental Protection Agency on Caesium-137 contamination:
People may ingest caesium-137 with food and water, or may inhale it as dust. If caesium-137 enters the body, it is distributed fairly uniformly throughout the body's soft tissues, resulting in exposure of those tissues. Slightly higher concentrations of the metal are found in muscle, while slightly lower concentrations are found in bone and fat. Compared to some other radionuclides, caesium-137 remains in the body for a relatively short time. It is eliminated through the urine. Exposure to cesium-137 may also be external (that is, exposure to its gamma radiation from outside the body).
Like all radionuclides, exposure to radiation from cesium-137 results in increased risk of cancer.
This is from the Union of Concerned Scientists:
Iodine-131 is one of the most radioactive isotopes released in a nuclear accident. It has a half-life of 8 days, meaning half of it will have decayed after 8 days, and half of that in another 8 days, etc. Therefore, it is of greatest concern in the days and weeks following an accident. It is also volatile so will spread easily. In the human body, iodine is taken up by the thyroid, and becomes concentrated there, where it can lead to thyroid cancer in later life. Children who are exposed to iodine-131 are more likely than adults to get cancer later in life. To guard against the absorption of iodione-131, people can proactively take potassium iodine pills so the thyroid becomes saturated with non-radioactive iodine and is not able to absorb any iodine-131.
Cesium-137 is another radioactive isotope that has been released. It has a half-life of about 30 years, so will take more than a century to decay by a significant amount. Living organisms treat cesium-137 as if it was potassium, and it becomes part of the fluid electrolytes and is eventually excreted. Cesium-137 is passed up the food chain. It can cause many different types of cancer.
New Scientist: How nuclear accidents damage human health.
Reuters has a report about food implications.