Hurricane Harvey has deluged America's fourth-largest city with devastating floods, with rising water forcing thousands on to rooftops and overwhelming rescuers receiving constant calls for help.

AMINEX plc, an Irish oil and gas explorer saw the sharpest rise in its share price in four years in London yesterday, after tests at the Sunny Ernst-2 well in Texas “materially exceeded expectations”, the company said.

Hospital and nursing home patients were evacuated and as many as one million others were ordered to clear out along the Gulf Coast today as Hurricane Rita intensified into a Category 4 storm with 140mph winds that could batter Texas and bring more misery to New Orleans by the weekend.

Hurricane Rita strengthened to a dangerous Category 3 storm early today, sparing the Florida Keys but prompting mandatory orders to once again evacuate New Orleans as well as the Texas city of Galveston.