Tens of millions of the worm-like larvae have appeared in the northern part of the country, where they are destroying green crops like cabbage and collard greens and contaminating the water supply, Liberian Information Minister Laurance Bropleh told CNN Wednesday from the capital of Monrovia.

"I am not aware that they have been here before, ever, and certainly not in this great number," Bropleh told CNN. "That is why it was so overwhelming initially when we first discovered it."

The state of emergency covers the three northern Liberian counties of Bong, Lofa, and Gbarpolu, Liberian officials said.

President Ellen Johnson Sirleaf told legislators Monday that 350,000 people in 62 communities in those three counties may have been affected.