A fresh aftershock, measuring 6.1 degrees on the Richter scale, shook the northeast Japanese province of Ibaraki on Saturday.

Authorities in Ibaraki released a statement announcing there had been no damage to any nuclear plants in the province, one of those most affected by the natural disasters of the past eight days.

The aftershock, which was also felt in Tokyo, took place at 6.56pm local time (09.56 GMT). The Japanese Meteorological Agency warned that the latest seismic activity could cause "minor changes" to sea levels, but that it was not expected to provoke a further tsunami.

Contaminated milk and spinach

Elsewhere, Japanese officials said that radiation levels in spinach and milk from farms near the nuclear complex exceeded government safety limits, even though they represented no immediate health risk.

The Vienna-based diplomat said the atmospheric measurements are 100 million to 1 billion times less than health-threatening levels.

He said the readings were taken on Friday at Takasaki, Japan, about 330 kilometers (200 miles) southwest of the accident site near the city of Fukushima; at Petropavlosk-Kamchatsky on Russia''s Kamtchatka Peninsula; and at Sacramento, California.

In Japan, tainted milk was found 20 miles (30 kilometers) from the plant, while the spinach was collected between 50 miles (80 kilometers) and 65 miles (100 kilometers) to the south, Chief Cabinet Secretary Yukio Edano told reporters in Tokyo.

While the radiation levels exceeded the limits allowed by the government, Edano said that the products "pose no immediate health risk" and that more testing was being done on other foods.