URGENT! Tame dwarf hamster became aggressive

[cypher]

That cage is very small so do try to get him something bigger as soon as you can, he'll be ok for a little while but he won't be able to do normal hamster things like digging, burrowing, running in the wheel in there as you need space for a good size house (a cardboard box will do) sandbath etc. Can you get a new wheel to put in the bin for him & make a cage out of that?
Your hams may not appear entirely happy for a short while, they need to adjust to the change but try not to worry just give them a little time.
You know they're happy when they're not appearing nervous all the time, they run in their wheels, eat & drink normally & just generally get on with doing hamster things! It is hard to explain but I think you can tell just from watching them when they're settled again.

[alpacassei]

Depending on how long it will be until you can buy a new wheel and bottle, you could put the old cage open inside the bin cage so he can still use his wheel and water bottle until you have the new ones.

Adding to what Cypher said, other signs hamsters aren’t happy are bar chewing, frequent scratching or digging and the sides/corners of the cage, excessively running around the cage with out a break, and over-grooming. Some hamsters will become less active and spend most their time asleep.

[Ashley Ash]

An update,I have mistaken the cage I wrote just now with my current one. The previous that you saw was a small,mine is a medium version of the cage. It has about 45cm (L) x 30cm (W) x 32cm (H) but I understand that it’s still kinda small for my hammy. I will try my best to get a new cage for him. Thanks for all the advices.