The language used by China's UN Ambassador Wang Guangya on Wednesday appeared to be the strongest yet by Beijing.
Wang made clear in an interview with The Associated Press that China opposes any move to expand the council now, because the 191 UN member states are deeply divided.
Brazil, Germany, India and Japan - known as the Group of Four or G-4 - circulated the resolution on 16 May and indicated they will put it to a vote by the General Assembly in June.
"I think what has been proposed by G-4 is very dangerous, so as far as China is concerned, we will work with others to see that this will not happen," Wang said in an interview.
He said the resolution would split the UN membership, and if the G-4 pushed for a vote "the whole atmosphere in this house is being undermined, is being destroyed".
Every member also has a different opinion on who should be permanent members, he said. China has opposed Japan's effort for a permanent seat, complaining about what many Asians consider Japan's lack of atonement for second world war abuses.
The result, Wang said, would be that UN members would not be able to discuss more important issues that Secretary-General Kofi Annan wanted included in a major overhaul of the UN.
After 10 years of debate, Annan told UN member states in March that he wanted a decision on council expansion before September, when he had invited world leaders to a summit to consider restructuring the global organisation.
"If it comes to the last stage ... I don't think they [China's legislature] will take a very positive action on this"
China's UN Ambassador
He suggested that if consensus were not possible, the General Assembly president should consider calling a vote.
There is wide support for expanding the Security Council, whose composition reflects the post-1945 era when the UN was created, to represent the global realities today. But the size and membership of an expanded council remains contentious.
Road to approval
The G-4 resolution needs to be approved by two-thirds of the 191 member states to be adopted, but that is only a first step.
New permanent members would then have to be elected by a similar two-thirds votes.
But the most difficult step is a final resolution to change the UN Charter, which not only requires a two-thirds vote but also approval by the Security Council's five permanent members who wield veto power - the US, Russia, China, Britain and France.
Wang said that "if it comes to the last stage, I'm sure our legislature would take into account the feelings of others - and I don't think they will take a very positive action on this".