Japan has paused for a minute silence one week on from the earthquake and tsunami that has devastated the country.

The alert level at a stricken nuclear plant has been raised from four to five on a seven-point international danger scale for atomic accidents.

The move places the crisis at the Fukushima Daiichi site two levels below Ukraine's Chernobyl 1986 disaster.

The head of the UN's nuclear watchdog warned in Tokyo meanwhile that the battle to stabilise the plant was a race against the clock.

Chris Hogg reports.