The question I'd be inclined to ask is why is the government refusing to accept assistance? It sounds to me like there is a targeted government policy towards inflicting such misery in the affected reason for more sinister reasons.
If it's however a capacity issue I'd argue there is a strong moral imperative to offer as much support as is feasible, even with regards to providing support to enable increased capacity to be able to handle any such support. I think the case of the Ottoman support to Ireland during the great famine springs to mind in this instance - I'd encourage you to check out the story:
Yes, it's a fascinating story (there is also the case of Choctaw support during the famine too - which I find more interesting, as the Irish didn't always have the most noble effect on native peoples on the other side of the Atlantic.) However, I didn't see it as necessary to include that as it wasn't a state intervention in a comparable way to that undertaken by the Ottomans.
I'm sure there are lots of examples in a number of contexts, and I'm sorry I can't provide more insight there - it's just I know this experience a little more.
Sovereignty in all cases is 100% respected by the Security Council of UN. The only expectation is Responsibility to Protect (R2P) [introduced in 2005] as a last resort but only in specific cases.
Probably the most prominent case to your question is Oil-for-Food Programme in Iraq. Although people were suffering famine, Saddam regime (legit government) declined UN intervention for many years. Even when he accepted, UN supervisors could enter only in designated ares with limited competences. Basically sovereignty and non-interference are cornerstones to the international relations which in the same time hold the structure but limit the quest for positive peace.
First, you need to be sure that there really is famine. Often, “humanitarian action” is used only as a pretext for intervention. In today's world, too many lies and not always an objective view is available. On the other hand, if this is true, it is not necessary to use marines, private initiatives can be supported.
Two dualities may lead to the answer rather than giving an answer:
First, it is a matter of starting point: how far morality allows to change morality (since there are multiple moralities). Thus, which morality has moral superiority upon another morality.
Second, the so-call institutional duality can facilitate the discourse and symbolic frames: economic morality determinins socio-political morality [e=f(s)] or social morality determins economic morality [s=f(e)].
If one can answer these questions, it is easy to answer those questions raised and answered. Why? The world view of morality changes with recognition of power, legitimacy and known vocabularies associated with these questions.
The question is more about practical morality rather than moral morality!