TOKYO (MarketWatch) -- The Tokyo metropolitan government said Saturday that elevated levels of radioactive cesium were detected in a herd of cattle from Fukushima prefecture, marking the first time that radiation has been found in domestic livestock since the start of the nuclear crisis in March.

The level of radioactive cesium detected in the group of 11 cattle exceeded Japan's safety standards by three to six times, a Ministry of Health spokesman said.

All cattle originated from the same farm in Minamisouma, which is in close proximity to Tokyo Electric Power Co.'s stricken Daiichi nuclear plant, he said. None of the cattle in question were made available to consumers, he added.

According to a representative at Fukushima Prefecture government's livestock division, the cattle came from the 20-30km evacuation preparation zone in Fukushima and had gone through and passed the mandatory screening test before shipment. The Fukushima government screening, however, was conducted before slaughtering and therefore only tested for external exposure, while the cesium found this time was on the actual meat after the cattle were processed in Tokyo.

"We are absolutely in shock that the internal radiation level was so high, because when we screened them, we got a zero cesium reading on their surfaces," the representative said. In addition to screening for external radiation, the prefectural government also examined how the cows were raised and what type of food they have been fed before giving the green light for shipment.

"They were raised indoors, and ate food and drank water that was deemed safe by current government standards," he said. Though this is the first time that excessive radioactive cesium was found in meat from Fukushima, radiation testing on the receiving end has been limited since the start of the nuclear accident. According to the spokesman at the Ministry of Health, monitoring on food radiation is done on a random basis before it is made available to consumers.

"Far less than 1% of all food (including meat, fresh produce and seafood) coming from Fukushima has been tested," he said, and there is no plan to change the current monitoring system.

Since late April, when the Fukushima government first imposed mandatory radiation screening on livestock, 2924 cows have been tested and shipped from the evacuation preparation zone in Fukushima, the government representative said. None have been banned based on their external radiation reading.

On the other hand, the ban on livestock shipments from the 20km evacuation zone in Fukushima is still in place, he noted. The government of Fukushima is currently asking farmers in Minamisouma to refrain from cattle shipments, he said, but no action has been taken on other livestock such as swine and poultry.