(Updates with casualties in town of Pilger)
June 16 (Reuters) - A swarm of tornadoes, some appearing two at a time, struck several farming communities in northeastern Nebraska on Monday, killing at least one person and injuring 16 others in one town that was especially hard hit, officials said.
The tornadoes, part of a super-cell thunderstorm system, appeared to be class EF-2 or EF-3 twisters, meaning they packed cyclonic winds of up to 165 miles per hour (265 kph), said Rich Thompson, the lead forecaster for the National Storm Prediction Center.
Thompson said the agency tracked at least four different twisters in northeastern Nebraska, with one or two occurrences in which a pair of tornadoes touched down simultaneously.
"Two powerful tornadoes on the ground at the same time is quite rare," said Barbara Mayes, a meteorologist at the National Weather Service office in Omaha, Nebraska.
Additional tornado activity was detected in central Nebraska, behind the first wave of storms.
Nebraska Governor Dave Heineman declared a state of emergency for the stricken region.
The Nebraska Emergency Management Agency has received reports of injuries and damage throughout Stanton, Cuming and Wayne counties in the northeastern corner of the state, spokeswoman Jodie Fawl said.
"We have had reports of people trapped in several of the communities," she said, adding that roads were closed to all but emergency vehicles near Pilger, which appeared to have sustained the greatest damage.
One person was dead and 16 injured from a tornado that struck Pilger, Stanton County Sheriff Michael Unger told Reuters. He said those hurt were taken to a hospital in nearby Norfolk, Nebraska, but did not know the nature or severity of the injuries.
A storm chaser video on the Weather Channel showed two large tornadoes in the same video frame tearing across primarily farmland near Stanton. (Reporting by Mary Wisniewski in Chicago and David Bailey in Minneapolis; Editing by Peter Cooney and Jim Loney)