Ukraine has 11 billion cubic metres (bcm) of natural gas in underground storage versus a government target of 19 bcm, the head of its gas transmission system operator said on Wednesday.

"This winter will probably be the most difficult in our history," Sergiy Makogon, chief executive of the transmission system operator, told a news briefing. "At the moment in underground storage sites there is around 11 bcm of the 19 (bcm) the cabinet wants."

Makogon said before Russia's invasion Ukraine used around 30 bcm a year of gas but that he expected consumption would shrink to around 21-22 bcm a year.

Ukraine's economy is expected to contract sharply as a result of the war, with the central bank predicting in April a gross domestic product fall of at least one-third in 2022.

Makogon said Ukraine needed to prepare itself for a future scenario where Europe stops buying gas from Russia.

"Our (transmission) system will no longer be necessary. We expect there will be no transit, we will look for other opportunities to use the system," he said.

(Reporting by Pavel Polityuk, Writing by Alexander Winning, Editing by Timothy Heritage)