An under-construction hotel complex in Saudi Arabia will feature the world's second-tallest building, topped by a clock six times bigger than London's Big Ben, said the hotel's general manager.

The Mecca Royal Clock Tower will be made up of 662 metres of concrete structure and a 155-metre crecent-topped metal spire, Mohammed al-Arkubi said at a press conference in Dubai.

Combined, the two parts of the tower in the Muslim holy city of Mecca would be only roughly 11 metres shorter than Dubai's Burj Khalifa, the world's tallest tower at 828 metres.

Even the concrete section of the Mecca Royal Clock Tower would be taller than the current second-tallest building in the world, the 508-metre Taipei 101 in Taiwan.

"The first part of the hotel will open at the end of June, while the clock will begin operating at the end of July," ahead of the Muslim holy month of Ramadan, which is expected to begin around August 10, Mr Arkubi said.

The German-made clock, billed as "the largest in the world", will have 45-metre wide and 43-metre tall faces on all four sides of the tower, he said.