Saudi Arabia hopes the four faces of the new clock, which will loom over Makkah’s Grand Mosque from what is expected to be the world’s second tallest building, will establish Mekkah as an alternate time standard to the Greenwich median.

The clock is targeted to enter service with a three-month trial period in the first week of the holy month of Ramadan on or about August 12, according to the Saudi state news agency SPA.

It boasts four glimmering 46 metre-across (151 feet) faces of high-tech composite tiles, some laced with gold, sitting more than 400 metres (1,320 feet) over the Holy Haram compound.

The tower’s height will reach 601 metres (1,983 feet), SPA said. On its website, Premiere Composite, which is responsible for cladding the top section, including a shimmering spire topped by a golden crescent moon, puts the planned height at 590 metres (1,947 feet).

That would make it the world’s second tallest building — ahead of Taiwan’s 509 metre (1,670 feet) Taipei 101, but well behind the Burj Khalifa, the 828 metre (2,717 feet) skyscraper inaugurated in Dubai in January.

Some 250 “highly qualified Muslim workers” were completing welding work on the clock’s frame, SPA said.

More than six times larger in diameter than London’s famed Big Ben, the clock faces, with the Arabic words “In the Name of Allah” in huge lettering underneath and will be lit with two million LED lights.

Some 21,000 white and green coloured lights, fitted at the top of the clock, will flash to as far as 30 kilometres (18.7 miles) to signal Islam’s mandatory five-times daily prayers.

On special Muslim occasions, 16 bands of vertical lights will shoot some 10 kilometres (6.2 miles) up into the sky.

“Everyone is interested to see the clock, despite the lack of sufficient information about it, and its mechanism,” said Mekkah resident Hani al-Wajeeh.

“We in Makkah hope to be the world’s central time zone, and not just have a clock to look at, to show off,” he said.

The developer of the massive seven-tower Abraj al-Bait complex had kept the details of the clock a secret, but it is visibly in place now, adorned with the green crossed sword and palm symbol of the Saudi state.

Mohammed al-Arkubi, the manager of the Royal Makkah Clock Tower Hotel in the building below, said the installation of the clock, its faces made by the German-owned Dubai company, Premiere Composite Technologies, has been “a huge operation.”

The clock reflects a goal by some Muslims to replace the 126-year-old Universal Time standard — originally called Greenwich Mean Time (GMT) — with Makkah mean time.

At a conference in Doha in 2008, Muslim clerics and scholars presented “scientific” arguments that Makkah time is the true global meridian. They said that Makkah is the centre of the world and that the Greenwich standard was imposed by the west in 1884.

Big does not begin to describe the Abraj al-Bait complex just across the street from the south gate of the Grand Mosque, the Muslim world’s most sacred site.

Built by a government-controlled fund, the complex sits seven huge towers atop a massive podium. Six are between 42 and 48 stories, and in the middle is the clock tower, appearing nearly twice as tall as the others.

Moreover, the entire complex, with 3,000 hotel rooms and apartments, a five-story shopping centre and gigantic prayer and conference halls, will give it 1.5 million square metres (16.1 million square feet) of floor space, according to architects and construction industry reports.

At that it will tie Dubai International Airport’s newest terminal three for the world’s largest building by floor space.

The complex will sport three top-class hotels, the Fairmont, Raffles and Swiss Hotel. It will also have hundreds of luxury apartments, most of them designed to have a direct view of the Grand Mosque.

The project is part of the Saudi government’s plan to develop Mekkah to be able to receive as many as 10 million hajj Pilgrims every year, up from the current three million capacity.

That is necessary to accommodate a rapidly growing global population of Muslims, who have a duty to make a pilgrimage to Makkah at least once in their lifetimes, if possible.

At the peak of the hajj, according to architect Dar al-Handasah, the complex should accommodate 65,000 people.

The clock will be the focus. Elevators will take visitors up to a huge viewing balcony just underneath the faces, and also a four-story astronomical observatory and Islamic museum.

“The construction of the biggest clock in the world in the purest spot on the earth is a dream-come-true for Muslims,” said Atif Felmban, who lives in the city.

“Before, we heard and saw famous clocks in the West. But today we can as Muslims be proud of this giant project,” said Ahmed Haleem, an Egyptian living in the Muslim holy city.

“I might leave Mekkah before the opening ceremony for the clock. But I will be keen to follow it and set my watch to it as soon as it is working,” Haleem said.

“It means an honour for a place, and time for me,” he said.