"We are trying to stop the leak right now and it is too early to say when the traffic will resume."
A Rotterdam port spokesman said that shipping has been halted in the area of Maasvlakte, which represents around one fifth of the total port area.
Earlier on Thursday the Dutch ANP agency said the fire department was trying to determine if the gas cloud is a danger to public health.
The 800 million euro Gas Access to Europe (GATE) terminal in the port of Rotterdam, was built by Gasunie and Koninklijke Vopak .
Rotterdam is the largest European port for the import of crude oil, and the biggest port for iron ore supplies to the German blast furnaces in the Ruhr region.