Eleven look like muscular males with painted yellow skin. The 12th is much slimmer and thought to be a woman, according to Zhang Tinghao of the Shaanxi Provincial Bureau of Cultural Relics.

The three restored figures lack their heads so it is hard to tell. Below their bare torsos, they wear short tunics painted with geometric designs. From their postures, experts think they were portrayed engaged in some sort of acrobatic feat. One figure holds his own wrist, another is lifting up one hand. The third figure, who is stout with strong arms and legs, appears to be grasping a short pump-like object.

'Acrobats were quite common in ancient China. From paintings at Dunhuang we know that when an important figure went out, he would have some acrobats accompany him to keep him amused on the road,' said Xu Pingfang, director emeritus at the Institute of Archaeology.

Experts at the Museum of Terracotta Warriors and Horses are not optimistic that they will be able to piece together the broken fragments to reassemble the acrobats' heads.

According to a newsletter Archaeology And Museum News, the figures were found during a trial excavation which uncovered a pit the size of a soccer pitch in the area between the inner and outer rectangular walls, which enclose the emperor's burial mound.

This area contains some 600 pits and tombs, which have barely been touched by archaeologists. Work has so far concentrated on the pits outside the walls where the terracotta warriors were discovered.

The latest excavation discovered three tunnels, one of which houses the acrobatic troupe, another a bronze tripod and a third has yielded nothing so far.

The pit is close to another discovery made this year, a chamber where stone armour was found. Initial digging has unearthed thousands of stone fragments once held together by bronze threads to form suits of armour.

'We've excavated a 100-square-metre area and found 25,000 pieces of stone that probably made up 70 to 80 sets of armour, including helmets,' said Guo Baofa who is in charge of preservation and restoration work.

The pieces of stone were found piled up roughly in circles and in layers, but this was not how they were intended to be found in the afterlife.

'The armour was originally hung up or supported somehow but collapsed,' he said. The team has restored one suit of armour out of 400 pieces of limestone which together resemble the plate-like suits modelled out of clay worn by the terracotta warriors. A stone helmet has been found.

Less than a third of the armour pieces are intact and nearly half were charred white or in fragments. Mr Guo thinks the storage chamber was lined with wood which burnt, turning it into an underground oven. The wood lining the walls and roof have been transformed into charcoal. Historical records report that the army led by Xiang Yu which overthrew the Qin Dynasty also set fire to the entire mausoleum.

The pit was discovered in 1997 after archaeologists went to investigate what was causing severe subsidence at a local farmers' orchard. Explorations began in autumn last year and a tunnel was found some five metres underground.

New discoveries are still being made about the original terracotta warriors, the newsletter reports, amidst controversy about careless preservation methods used in the past.

In May a kneeling archer was uncovered in Pit No 2 which experts say is the most colourful figure ever discovered. He is clad in dark brown armour and decorated with red sashes and belts.

It is now clear that the warriors were never brown, as they now appear, but brightly painted. Even the eyeballs were painted with black pupils and they had complexions of powdered orange.

Archaeologist Zhu Yonghong believes Qin soldiers were never issued with uniforms but wore homemade garments and that is why there is a great variety of colours found on the models. Only a few traces remain but they show the soldiers wore garments dyed red, green, yellow, blue, purple and many other colours.

Their earth colour is blamed on the fact they were burnt, but it also seems clear what colour remained peeled off or faded when the warriors were exposed to air and light.

'Now we are more cautious and more experienced. Before we simply scraped off the dust and mud from the terracotta. We would not do it that way now,' said Mr Xu.

Some of the statues have begun to go moldy in the moisture and warm temperatures generated by the crowds of visitors to the buildings housing them. Since 1979, 34 million people have visited.

A new method of preserving the surface of the warriors has been developed by a Sino-German team. It involves treating the surface with an emulsion of polyurethane and polyethylene glycol.

'But we still don't know how long we can preserve the colours, so the policy is not to excavate too many more figures. Until we find better ways, it is still safer to leave them underground,' Mr Xu said.