Work has begun at Chernobyl in Ukraine to move a giant shield over the remains of the reactor, which lost its roof in a catastrophic explosion in 1986.

The concrete and steel arch measures 275m (900ft) wide and 108m (354ft) tall and has cost $1.6bn (£1.3bn) to construct.

The European Bank for Reconstruction and Development (EBRD), which is leading the project, describes the arch as the largest moveable land-based structure ever built.