Flames could be seen erupting from the Urengoy-Pomary-Uzhgorod Pipeline in central Ukraine. No one was reported injured by the explosion.
It is not clear what caused the blast. European and Russian companies said gas exports to the EU were not affected.
On Monday, Ukraine said Russia had cut off gas supplies to the country following a dispute over gas payments.
Hundreds of lives have been lost in fighting in Ukraine’s eastern Luhansk and Donetsk provinces, where pro-Russian rebels are battling government forces after declaring independence just over a month ago.
The blast took place at the pipeline, which is also known as the Trans-Siberian Pipeline, in Poltava province on Tuesday.
Ukraine’s gas transport monopoly, a Slovak gas transit firm, and sources at Russian gas producer Gazprom, all told reporters that the transit of gas to Europe would not be affected.
“Exports have not been cut. There is a parallel pipeline,” the Gazprom source said.
According to AFP news agency, Ukraine’s state emergencies service said it appeared to have been the result of a puncture or loss of pressure.
However, the energy and interior ministries said it could have been an attempted terrorist attack, Reuters reported.
Interior Minister Arsen Avakov said: “According to local residents, they heard two big bangs just before the explosion which could indicate they were deliberate explosions.”
The energy ministry said: “It is not the first attempted terrorist attack on the Ukrainian gas transportation system.”
Also on Tuesday, a Russian state TV journalist was killed in a mortar attack near a village outside the city of Luhansk, Russian media reported.
Igor Kornelyuk died in hospital after the attack near Metalist while a colleague, sound engineer Anton Voloshin, was reported missing.
Moscow condemned the killing of the journalist, describing it as a “crime of Ukrainian forces”.
Last month, Italian photojournalist Andrea Rocchelli and prominent Russian human rights activist Andrey Mironov, who was accompanying him, were killed by mortar fire in eastern Ukraine.