Texas is bracing itself for Hurricane Harvey, which may be the worst storm to hit the US mainland in 12 years.

Harvey, currently a category two storm in the Gulf of Mexico, is expected to make landfall on Texas' central coast late on Friday or early Saturday.

The National Hurricane Center said storm surges may bring life-threatening floods in and around Houston.

The storm may bring 97 cm of rain, 210km/h winds and 3.5 metre storm surges, say forecasters.