Japan's attack on Pearl Harbour started the Pacific War. On the morning of 8 December 1941, Japanese marines occupied the International Settlement. CriticalPast have posted a video of the Japanese film of the Japanese troops fanning out over the city.
The only battle was when the Japanese Navy boarded the HMS Peterel under a flag of truce and demanded her surrender. Lieutenant Polkinghorn in the best British tradition told them to "Get of my Bloody Ship". A few minutes later, the Japanese cruiser Idzumo opened fire on the Peterel which much outgunned was sunk soon after. Polkinghorn survived and eluded capture throughout the war. USS Wake, an American gunboat, was captured without a fight.
In Gunboat Justice I wrote about the takeover of the settlement and how it effectively ended British and American extraterritoriality in occupied China. The video is fascinating as it brings this event to life. It shows in addition to various shots of troops patrolling streets while daily life appears to go on: the Bund in the early morning sunlight (0:12) Japanese marines pouring over Szechuan Road Bridge in trucks (0:20); the now occupied American Club with a Japanese flag flying over it on Foochow Road (0:25 and 1:15); a glimpse of a C. Ingenohl cigar shop (which I wrote about in Ch. 47) (0:55); the remains of HMS Peterel (1:56) and the now captured USS Wake flagged with a Japanese flag (1:58).
The judges and staff of both the British and American courts were interned for 6 months in Shanghai before being repatriated.
I have read a lot about the occupation, but being able to see it in a film brings a whole new complexion to what occurred.