A "large explosion" cut the pipeline, which carries Siberian gas through Ukraine to Germany and other EU clients, said Viktoria Ruban, spokeswoman for the Ukrainian emergency situations ministry.
The blast occurred at about 1125 GMT close to the village of Luka on a section south of the Ukrainian capital Kiev, tearing out a 30-meter (32-yards) length of pipeline and hurling debris 150 meters (yards), she said.
"It's one of the most serious accidents in recent years," an official from the Ukrainian state gas company Naftogaz told AFP on condition of anonymity.