The flow of gas through a section of the Urengoi-Pomary-Uzhhorod pipeline that takes gas from Russia's Arctic to Europe via Ukraine had been halted at 1050 GMT, the local officials said on the Telegram messaging app.
Oleg Nikolayev, governor of the Republic of Chuvashia, told state TV that three people, who were carrying out servicing work, died in the accident, while another, a driver, "was in a state of shock".
He said it was unclear when gas supplies via the pipeline could resume, and authorities were trying to work that out.
The Chuvashia regional Emergencies Ministry said an explosion had ripped through the pipeline during planned maintenance work near the village of Kalinino, about 150 km west of the Volga city of Kazan. It said the resulting gas flare had been extinguished.
The pipeline, built in the 1980s, enters Ukraine via the Sudzha metering point, currently the main route for Russian gas to reach Europe.
Europe's gas prices have surged this year after Russia cut exports through its main gas pipeline route into Germany, leaving only pipelines via Ukraine to ship Russian gas to European consumers.
Gazprom said earlier on Tuesday it expected to pump 43 million cubic metres of gas to Europe via Ukraine through Sudzha in the next 24 hours, a volume in line with recent days.
Forward prices on the Dutch TTF hub rose following the news. The benchmark TTF front-month contract was up 1.10 euros to 108.10 euro per megawatt hour by 1347 GMT. It had traded around 105 euros/MWh earlier in the day.
