Nuclear fuel has melted through base of Fukushima plant - Telegraph

In early April, the agency said some 370,000 terabecquerels escaped from the facility. It now believes that figure was 770,000 terabecquerels.

That's now 15% (and the origial figure was more like 7%). Interestingly, another government agency got out a number closer to the current NISA figure based on the emissions:

Fukushima nuke crisis upgraded to '7'

According to the agency, the total amount of iodine-131 and cesium-137 emitted between March 11 and at 11am Tuesday reached 370,000 terabecquerels according to the reactors' estimated condition. Within this assessment, cesium levels were converted to their equivalent in iodine-131 levels.

The Cabinet office's nuclear safety commission, meanwhile, announced Tuesday that the total amount of iodine and cesium emitted between March 11 and April 5 was 630,000 terabecquerels (again, with cesium levels converted to the iodine equivalent), calculated according to the amount of radiation observed around the facility.

...In the Chernobyl crisis, about 5.2 million terabecquerels of radioactive material was emitted into the air in the space of 10 days.