A prominent Israeli rabbi has urged farmers to pray that no more locusts reach the country as a modern-day biblical plague of one million of them spreads across the Holy Land.

Eliezer Wimcha Weiss quoted a Jewish law, Shulchan Aruch, that said that if "even one wing" of a locust were seen, residents should start praying to avoid more harm to the harvest.

Recalling the biblical plague that struck Egypt during the exodus of Israelite slaves, locust clouds have been darkening the skies, three weeks before the Jewish festival of Passover.

Officials said the swarm covered nearly 2,000 acres of desert overnight.

Israel's agriculture ministry is adopting a more secular approach to the issue by spraying pesticides.

"We hope our actions are effective," one pilot said on army radio. "Let's hope the damage will be minimal."

Locusts, which tear through crops destroying entire harvests, last invaded southern Israel in 2004.

Residents of Ramat Hanagev have sealed their homes against locusts. One homeowner of nearby Ramat Gan told the Jerusalem Post that that he had found a locust on his terrace.

"I stepped on it when I went to move my plants from the living room window into the kitchen," he said. "[I was] following an inner voice that told me to protect them in case the locusts arrived at Ramat Gan at night when I was sleeping or when I was at work the next day. I did not want to abandon the tulips."