Trump, who was supposed to boycott the Climate Action Summit, unexpectedly dropped in to hear Modi on Monday.

The US President who had participated in the 'Howdy, Modi!' rally in Houston on Sunday and effusively praised his leadership, had scheduled a meeting on Global Call to Protect Religious Freedom to around the time the summit was still going on.

The religious freedom meeting was seen as an attempt by Trump to draw attention away from the climate summit.

But continuing their friendliness from Sunday, he stopped by as Modi was speaking.

He heard Modi say that not enough was being done to fight climate change.

"Various efforts are being made by different countries to fight climate change but it has to be accepted that if we have to overcome a serious challenge like climate change, what we are doing at the moment is just not enough," he said.

Trump, who is considered a climate change sceptic, has withdrawn the US from the Paris climate change accord and rolled back several measures taken by previous US administrations and states to fight global warming.

Approach to climate change is one of the areas of difference between Modi and Trump.