Reason for increase to level 5 on scale-

"The provisional evaluation stands at level 5 for the No. 1, No. 2 and No. 3 reactors, as their cores are believed to have partially melted and radiation leaks continue, Japan's nuclear safety agency said.
"The agency set the level at 3 for the plant's No. 4 reactor, where an overheating spent fuel pool is also posing risks, and two reactors at the power plant that were undergoing maintenance when the quake struck."
Japan Times, Sat. 19, 2011, "Workers Battle Against Time."

http://search.japantimes.co.jp/cgi-bin/nn20110319a1.html

Two diagrams with the article show routing of reconstructed power cables from the switching station.

I had seen some statements about possible meltdown at three reactors; I had discounted them because of relatively low levels of radiation outside of the plant. Looks like there is still some question, but the paper indicates possible partial meltdown.