At least two persons have so far died in Southeast Texas as Hurricane Harvey, the most powerful storm to hit the state in more than 50 years, roared inland.

More than 1,000 people have been rescued in flooded parts of the capital, Houston, causing a flash flood emergency, as called by the National Weather Service (NWS).

The NWS says it has recorded 24.1 inches of measured rain in the past 24 hours and there have been more than 2,000 calls asking for help.

Flooding in Houston is, however, expected to worsen and is said to be well on its way to becoming historic, with potentially significant flooding expected in other saturated areas of Southeast Texas.

Forecasters have warned people not to travel unless they are fleeing an area subject to flooding or under an evacuation order.

People are also warned to move to higher ground amid an extremely dangerous and life-threatening situation.