"If we get a very cold winter, we have a problem," Bundesnetzagentur boss Klaus Mueller said in an interview with the Handelsblatt business daily.

Germany is racing to meet its gas storage targets in time for winter. Russia's Gazprom cut off deliveries to Germany via the Nord Stream 1 pipeline on Aug. 31 after reducing flows in June.

"By having well-filled storage facilities, we can buy ourselves more time for longer preparation for a gas shortage," Mueller said in an interview. "However, we cannot predict gas consumption more than a week and a half in advance. This is mainly due to the weather forecasts."

Gas storage were at nearly 89% capacity as of Sept. 14 as Germany aims to reach 95% capacity by Nov. 1.

Private consumer behaviour and circumstances in neighbouring countries will also help determine whether Germany suffers a shortage, Mueller said.

"There have already been more gas outflows in the past few days than I had hoped," Mueller said.

"In view of the warm temperature and the extremely high gas prices, I was very surprised. That has to change."

(Reporting by Miranda Murray; editing by Rachel More and Jason Neely)