The discovery shows the urgent need for Japan to take measures to stop the spread of genetically modified plants, said Masaharu Kawata, a Yokkaichi University lecturer.

Eight soybean plants engineered to resist a herbicide and one corn plant resistant to insects were found growing near roads at Shimizu port 150 kilometers (95 miles) west of Tokyo, Kawata said in his paper posted on the Internet.

"Spontaneous growth has been seen clearly in port areas and effective counter-measures must be addressed urgently," he wrote.

Japan imports genetically modified food mainly for feed or to make oil and soy sauce. But no farmer has planted the crops in Japan amid consumer fears about their safety.

While there were no further details about how the seeds spread, the agriculture ministry said it was not overly alarmed. "Corn and soybean need to be raised in a human-managed environment or they do not prosper," said ministry official Masato Fukushima. "It is possible that spilled seeds take root but it has not been known that they spawn a next generation."

In June the ministry said it had found that some imported genetically modified canola seeds had taken root in the wild in Kashima port, 100 kilometers (60 miles) east of the capital.

CAPTION Syringe in a corn ear symbolizing genetically modified organisms.