A swarm of hundreds of earthquakes that has been striking a corner of the Nevada desert near the Oregon border for months has intensified in recent days, prompting new warnings from seismologists.

About 750 earthquakes, mostly magnitude 2.0 to 3.0, have struck the area about 50 miles southeast of Lakeview, Ore., since the swarm started in July, said Ian Madin, chief scientist for Oregon's Department of Geology and Mineral Industries.

The temblors have been growing steadily stronger with time. Six earthquakes of magnitude 4.0 or greater have struck the area since Tuesday and about 40 have struck in the last 24 hours, Madin said.

"This week it has just gone crazy," Madin said.

The swarm is beneath an uninhabited part of the Nevada desert near the Sheldon National Wildlife Refuge, but officials are telling the public, especially the almost 2,300 residents of Lakeview, to develop earthquake plans if they haven't already.

"If you are not ready for an earthquake, now is an awfully good time to get ready for an earthquake," said Alison Ryan, a spokeswoman for the department.

Scientists believe groundwater is slowly percolating along the faults and building up pressure, making movement on the faults much easier, said John Vidale, director of the Pacific Northwest Seismic Network at the University of Washington.