New York, Sep 22 (DPA) The US and China committed to tackling their greenhouse-gas emissions blamed for global warming and asked each other to do more to halt the rise in global temperatures, at the start of a one-day UN summit on climate change

Tuesday.

US President Barack Obama acknowledged his country has been slow to respond to the threat of climate change, but said: 'This is a new day.'

'We understand the gravity of the climate threat. We are determined to act,' Obama said, noting efforts by his own administration to reduce vehicle emissions and promote renewable energy.

Obama has come under pressure from other countries as major legislation to curb US emissions has stalled in the Senate. But Obama said it was up to all major polluters to take action.

He called on other countries - especially emerging economies like China and India - to make the commitments necessary to lower their own growing emissions, in order to reach agreement on a new global deal by a crucial UN summit in Copenhagen in December.

'We cannot meet this challenge unless all the largest emitters of greenhouse-gas pollution act together. There is no other way,' Obama said.

Chinese President Hu Jintao said his country was determined to lower its burgeoning levels of greenhouse-gas emissions, but tasked richer nations with helping the poor adapt without destroying their economies.

'China has taken and will continue to take determined and practical steps to tackle this challenge,' said Hu, who is the first Chinese leader in 30 years to join the annual opening of the UN General Assembly.

'We should combine our efforts to address climate change with those to promote the growth of developing countries,' he said.

How much wealthy countries should give developing nations to lower their own emissions has been a key disagreement as government negotiators try to hammer out a new global climate treaty.

China has proposed that wealthy nations dedicate 1 percent of their gross domestic product to helping developing countries tackle global warming.