Two chunks of ice together measuring almost 20 square kilometres have broken off an Arctic ice shelf, the biggest break-up of Arctic ice in three years, Canadian officials announced.

Two floating islands of ice - measuring four to five square kilometres and 14 square kilometres - formed after the chunks broke from the Ward Hunt Ice Shelf off Ellesmere Island in the Canadian Arctic Archipelago, officials said.

"The first broke off sometime around July 22 and the second in the night of July 23 to 24," Luc Desjardins, a senior iceberg forecaster for Environment Canada's Ice Service, said.