Greenpeace activists hang from Houston bridge in protest ahead of Democratic debate

Twenty-two Greenpeace USA protesters climbed the Fred Hartman Bridge over the Houston Ship Channel, aiming to shut down the transport of oil and gas through the channel, the non-profit group said Thursday.

The climate crisis has emerged as one of the preeminent issues in the Democratic nomination fight, with polls showing it among the top -- if not the top -- issue on the minds of Democratic voters. Each of the top tiered Democratic candidates have released sweeping proposals to combat climate change, with key differences in how each would pay for their plans.

"We challenge every candidate on stage tonight to promise to hold the fossil fuel industry accountable if they become president," Greenpeace USA said on Twitter Thursday, ahead of all the top contenders in the 2020 Democratic field meeting at Texas Southern University.

The group called on leaders to commit to the Green New Deal and "embrace a just transition to renewable energy."

"We're in a climate emergency created by fossil fuel CEOs and made worse by (President Donald) Trump," Annie Leonard, the organization's executive director, said in a statement Thursday. "We can either take bold action to combat the climate crisis today or suffer the consequences — more floods, more mega-storms, and more fires — for years to come."

Local law enforcement is on the scene and vehicle traffic is moving across the bridge. CNN has reached out to La Porte Police.

During a news conference Thursday, Harris County Sheriff Assistant Chief Tim Navarre said that a call came into police as a "wreck on the bridge."

Navarre said the incident turned out to be a van full of protesters that stopped on the bridge and caused an accident.