For decades, the Amaravati sculptures, a stupendous collection of early Buddhist art considered one of the greatest treasures in the British Museum, have been poorly lit and difficult for visitors to see close up.

On Thursday, they will be displayed in their full glory when the central London museum reopens its largest gallery to the public after a two-year renovation.

Shiva Nataraja, Lord of the Dance. Photograph: British Museum

The newly improved Sir Joseph Hotung Gallery of China and South Asia will allow a different story to be told, curators say, with some objects going on show for the first time.

“It is the longest gallery in the museum. It’s 115 metres – as long as a football pitch – and the idea is to make it less daunting and more accessible,” said Jane Portal, the keeper of the department of Asia.

The refurbishment and redisplay means the Amaravati sculptures, which are held in a separate room at one end of the gallery, can be seen from the other. “They are just as important as the [Parthenon] marbles but people don’t know about them so much,” Portal said.

T Richard Blurton, the head of the museum’s south Asia section, added: “To be able to show it in a more dramatic way, and without any of the clutter which used to be here, is an enormous advance for us.”

A two-sided limestone relief from the Great Shrine at Amaravati. Photograph: British Museum

The stone sculptures, of which there are more than 120, date from the first century AD to the third, and adorned a fence around the Great Shrine of Amaravati, one of the most important Buddhist monuments in the world. They are the largest group of early Indian sculptures outside south Asia.

The refurbishment has been funded by Hotung, 25 years after he donated money and objects for the gallery to be opened in his name. “To do it twice in your lifetime is an amazing thing,” Portal said.

It has been a large project that included the replacement of wiring, heating, flooring and the air circulation system as well as repairs to gold leaf on the ceiling.

A Ming jar. Photograph: British Museum

Instead of thematic displays, the story of China and south Asia will be told chronologically to the present day. The oldest objects from China date from 5000BC; from south Asia (modern day India, Pakistan, Bangladesh and Nepal) the earliest material dates to 1.5m years ago.

Paintings and textiles that are rarely, if ever, displayed because of their fragility can at last be shown thanks to changes to the museum’s lighting.

These include Buddhist paintings that were discovered in 1907 in a hidden library in the Mogao caves, near Dunhuang in north-west China. Dating from AD910, they were among documents and manuscripts sealed away and unknown for hundreds of years. The plan is to rotate the paintings every six months.

Ceramic dragon tiles. Photograph: British Museum

The gallery, room 33, was reopened by the Queen on 8 November, exactly 25 years after she opened it for the first time. The completed gallery will open to the public on Thursday.

The refurbishment has, however, presented a problem for the museum: objects from south-east Asia – including Vietnam, Cambodia, Myanmar and Indonesia – have now been lost from public display in room 33. What happens to them remains to be decided.