On April 26, 1986, a botched test at the Soviet nuclear plant sent clouds of smoldering nuclear material across large swathes of Europe, forced over 50,000 people to evacuate and poisoned unknown numbers of workers involved in its clean-up.

A concrete sarcophagus was hastily built over the site of the stricken reactor to contain the worst of the radiation, but a more permanent solution has been in the works since 2001.

Easily visible from kilometers away, the 36,000 tonne 'New Safe Confinement' arch has been slowly pulled over the site over the past four days to create a casement to block radiation and allow the remains of the reactor to be dismantled safely.

On Tuesday, a ceremony was held at Chernobyl to mark this major milestone in the decades of work to secure the site that has been funded by donations amounting to over 2 billion euros ($2.1 billion) from over 40 countries and organizations.

"Let the whole world see today what Ukraine and the world can do when they unite, how we are able to protect the world from nuclear contamination and nuclear threats," Ukrainian President Petro Poroshenko said