TOKYO — Government officials on Saturday ordered more tests after detecting elevated levels of radiation in rice crops near the crippled nuclear power plant at Fukushima.

Radioactive substances have already been discovered in beef, milk, spinach and tea leaves, leading to recalls and bans on shipments. But officials have been especially worried about rice, a staple that makes up a significant part of the Japanese diet. Japan grows most of the rice that it consumes.

Preliminary tests on rice from paddies in the city of Nihonmatsu, about 35 miles from the Fukushima plant, showed the crops contained 500 becquerels per kilogram of radioactive cesium, prefectural officials said. Under recently adopted Japanese regulations, rice with up to 500 becquerels per kilogram of radioactive cesium is considered safe for consumption. (A becquerel is a frequently used measure of radiation.)

As a result of the latest findings, officials in Fukushima have ordered further checks on rice from the area, and they may ban shipments if similarly high levels of radiation are found again, prefectural officials told reporters.