The Labour Ministry has announced that businesses employed 686,246 foreign worker numbers as of October 2011, a rise of 5.6% from the same period last year. A total of 116,561 busineses reported employment of foreign workers, which is 7.2% up from last year. By nationality, Chinese were by far the largest group at 297,199, which is 43% of the total. 38.7% of these workers are employed at manufacturers. The Nikkei speculates that demand prompted by the aftermath of the earthquake may have led to an increase in short term contracts. Data from the Labour Ministry has been collected since 2007, when the law changed, obliging employers to notify the authorities of their foreign workers. These numbers won't necessarily tally with immigration records kept at the Justice Ministry, not least because information is taken at different points in time. I suppose it's also possible that more firms are recognizing their obligation to report foreign employment numbers, which may distort early trends in this dataset. Nevertheless, the figures make an interesting counterpoint to the view the the quake led many foreigners to leave Japan as work opportunities dried up.
Source (Japanese)