U.S. President Donald Trump blasted the climate change proposals of his Democratic challengers for the White House on Wednesday as they began showcasing their plans in a marathon round of televised town halls.

"The Democrats' destructive 'environmental' proposals will raise your energy bill and prices at the pump," Trump said in a series of tweets, just minutes after the seven-hour event kicked off on CNN.

Former Obama administration Housing Secretary Julian Castro was the first of 10 Democratic presidential contenders to explain plans to tackle climate change in the forums likely to pit moderates like front-runner Joe Biden against progressives such as Sens. Bernie Sanders and Elizabeth Warren.