An Australian emergency service worker on the ground in Texas says Houston looks like a 'city of islands' as Tropical Storm Harvey continues to bring torrential rain to the region.
Justin Back is the regional vice president of Acadian Ambulance, a privately owned company that provides emergency assistance during natural disasters.
He has lived in the state of Louisiana for five years, but has been sent to Houston to help deal with the skyrocketing demand for help.
"[Conditions are] tough and getting worse. The problem is it's not moving, or it's moving only very very slowly," Mr Back said.
"So there's just huge amounts of rain being dumped in one concentrated area at a time."
Mr Back is the son of former West Australian Liberal senator Chris Back, and served in the Australian Army for eight years before moving to the United States.
"Texas has a bigger population than Australia, and a huge part of that is concentrated along this coastline," he said.
"So when you have a storm of this size hit then it's obviously going to impact millions of people."
As rain continues to fall, Mr Back said it was becoming increasingly difficult to reach people in need and the state had declared a state of emergency in affected areas.
"Everything that can be done is being done," he said.
Civilian-led Cajun Navy head to the rescue
Forecasters say they expect another metre or more of rain to fall in the Houston area in the coming days, adding to an already catastrophic flooding situation.
"This event is unprecedented and all impacts are unknown and beyond anything experienced," the National Weather Service said on Twitter.
Mr Back said already a number of hospitals and nursing homes had been evacuated, and members of the public were banding together to help with water rescues.
"In Louisiana, where the Cajuns are from, we have a thing called the Cajun Navy," he said.
"It's just a big group of people with powered watercraft who respond voluntarily, at risk to themselves certainly.
"They come to areas of impact, and I think this may be the first time they've deployed to Texas — but it's a godsend certainly."
Mr Back said he expected conditions would worsen in the coming hours.
"It's all hands on deck," he said.
"As we speak, this is a very violent weather system.
"The building I'm in, we're sandbagging up the entryways as we speak and there's a very, very intense system about to hit us again from the south — it only builds and builds.
"We expect a very rough night tonight and it's just going to be this way until this weather system moves off us onto somewhere else, or back over the coast.
"The mood at the moment is one of survival and organisation and response and recovery, the rest of it will follow as it does.
Economic impact from hurricane
Houston is considered the "energy capital" of America and the site of US headquarters for Australian companies including BHP, Santos and Woodside.
Texas is also key to the US agriculture industry with extensive farmland across the state.
Mr Back said the storm would likely have a significant economic impact that could spread well beyond Texan borders.
"This could create a squeeze on the availability of the energy supply — the oil based energy supply," he said.
"That's obviously going to have an impact on prices."
He said while it was difficult to forecast the overall impact as it was impossible to know how long the recovery would take.
"I mean, Houston looks like city of islands at the moment.
"[The] whole coastal areas have been just so severely damaged, that it will be months, not weeks, before they make a full infrastructure and economic recovery."