The Reorganised National Government Of China, Japanese puppets based in Nanjing and headed by Wang Jingwei, declares war on the Allies.
Emily Hahn belives that this is the signal for the 'reign of terror' - intensified Kempeitai activivity against spying and illegal relief work - that is to see many of the so far uninterned 'Europeans' arrested, tortured, in some cases executed, and the rest sent into Stanley during the summer.
However, Hahn misdates Wang Jingwei's declaration of war to February, and the first arrests of the 'reign of terror' don't, to the best of my knowledge, take place for about a month, so I've followed Philip Snow in dating the start of the Kempeitai campaign to February: http://gwulo.com/node/14095
But in Shanghai the declaration of war does change things, and 'enemy aliens', some of whom have gone there from Stanley Camp, are interned in various camps between February and April. One of these was Salvation Army Brigadier C. K. Begley, who'd been sent from Hong kong to Shanghai to be reunited with his family, all of whom ended up in Yang Chow Camp near Nanking (now Nanjing.)
Source:
Hahn: Emily Hahn, China To Me, 1944 ed., 386