Tonga says tsunami was 'unprecedented disaster'

Four days after a volcano erupted and a tsunami hit, Tonga says it has suffered an "unprecedented disaster". New Zealand is leading the relief effort. We have an interview with the defence minister.

Also in the programme: the Mexicans searching for some of the tens of thousands who've disappeared during the drugs wars; and a new technique to purify water - using food waste.

(Photo: Aerial images show Tonga covered in volcanic ash. Credit: EPA)