G20 summit: Donald Trump thanks his 'haters' and says there is 'much to discuss' as he meets Vladimir Putin

US President Donald Trump is set for a day of tense talks with G20 leaders as he meets Russian President Vladimir Putin.

According to reports, the pair "shook hands and said they'll see each other soon" as they prepare for a head-to-head on Friday afternoon. 

Mr Trump will sit down with Mr Putin for the first time on Friday afternoon, an encounter that will be intensely scrutinised following allegations by US intelligence agencies that Moscow meddled in the US election to help Trump win.

It came as leaders from the world's top economies prepared for tough talks with Mr Trump on climate change and trade on Friday as the G20 summit got underway in Germany amid the threat of violent protests.

The meeting in the port city of Hamburg comes at a time of major shifts in the global geo-political landscape, with Mr Trump's "America First" policies pushing Europe and China closer together.

He spoke in Warsaw, Poland, on Thursday to a rapturous audience, and on Friday morning tweeted of already-successful meetings with leaders from other countries as the summit began. 

He added that he and Mr Putin had 'much to discuss'.

The summit also brings together Mr Trump and Chinese President Xi Jinping at a time when Washington is ratcheting up pressure on Beijing to rein in North Korea after it test-launched an intercontinental ballistic missile and threatening the Chinese with punitive trade measures.

Amid the big egos and seemingly intractable conflicts, the host, German Chancellor Angela Merkel, faces the daunting task of steering leaders towards a consensus on trade, climate and migration - all issues that have become more contentious since Mr Trump entered the White House half a year ago.

Mr Trump's bilateral with Mr Putin was scheduled to take place just 15 minutes after the start of the discussion on climate, a scheduling conflict that could complicate a deal.

"Merkel, as the G20 host, must not sacrifice ambition for unity. Instead, we need a G19 commitment to climate action that demonstrates the intent to implement and even go beyond what 195 nations agreed to in Paris," said Jennifer Morgan of Greenpeace, referring to the climate accord Trump has pledged to leave.

Facing her own election in two months, Mrs Merkel met with Mr Trump for one hour at a hotel in Hamburg on Thursday evening to try to overcome differences that envoys have been unable to settle in weeks of intense talks, including a last minute trip to Washington by the chancellor's top economic adviser.

The two leaders shook hands and smiled for the cameras, showing none of the tension that hung over their first two meetings, in Washington in March and on Mr Trump's first trip to Europe in May. After that, the usually cautious Mrs Merkel said the United States was no longer a reliable partner and urged Europe to take its fate into its own hands.