FRANKFURT, Sept 4 (Reuters) - Transatlantic shipping freight rates have come under pressure from slack demand, meaning ship operators must watch costs, the chief executive of Germany's Hapag-Lloyd said on Monday.

"Rates have definitely collapsed, and that means we have to start looking at our costs, which have gone up," said Rolf Habben Jansen, CEO of Hapag-Lloyd, the world's fifth biggest container liner, in a call with journalists.

He listed higher wage inflation, fuel prices, and terminal and timecharter costs, adding that the cost concerns could mean that certain voyages were cancelled.

(Reporting by Vera Eckert, editing by Miranda Murray)