Hurricane Harvey: Catastrophic flooding, National Guard deployed

Houston residents are dealing with catastrophic flooding, despite Hurricane Harvey being downgraded to a severe storm.

The fiercest hurricane to strike the US in more than a decade has left several dead and countless others homeless.

The National Guard is being deployed to aid rescue efforts after the greater Houston and Galveston area took on over 61cm of rain over 24 hours. 

The National Weather Service has warned of "additional catastrophic, unprecedented and life threatening flooding" into the next week, and enacted flash-flood emergency warnings for all of southeast Texas.

Questions are being raised as to why the city wasn't evacuated, but Houston Mayor Sylvester Turner is defending his decision to instruct residents to stay put.

Speaking at a news conference, Mr Turner said nobody was sure exactly where the storms would hit.

"No one knew where this storm was coming. If you'd gone to San Antonio, you'd run into rain. Same thing in Austin."

He also said a mass evacuation would have clogged the roads.

"If you give an order to evacuate, you create a nightmare."

The City of Houston tweeted early Sunday morning (local time) saying 911 services were at capacity and asked for those who can shelter in place, to please do so.

They say their dispatchers are overwhelmed with the number of calls coming in. Officials are pleading residents not call 911 unless a life is in danger.

Officials assisted in more than 500 rescues overnight, and hundreds of other community rescues occurred.

Many people are reportedly still trapped.

Officials are warning residents to not stay in their attics to avoid rising floodwaters.

Houston Police Chief Art Acevedo tweeted: "We have reports of people getting into attic to escape floodwater. Do not do so unless you have an ax or means to break through onto your roof."

The National Weather Service Houston echoed this message in their emergency bulletin, saying:

Mr Acevedo requested that Houston residents stay off the roads as much as possible.

With strained emergency services, desperate Houston residents are turning to Twitter for rescue.

After thousands of retweets, Ms Willis shared that her family was safe.

Hundreds of first responders are risking their own lives as they answer the calls for help.

President Donald Trump spoke with top administration officials via conference call on Sunday.

The White House says Mr Trump, Vice President Mike Pence, members of the Cabinet and other senior officials discussed federal support for response and recovery efforts.

Mr Trump announced he is planning to visit Texas soon.