Oil prices tumbled on Wednesday as vote counting showed Republican Donald Trump edging ahead in an unexpectedly tight US presidential election, setting world markets on edge.

Crude futures markets roared into action as Trump surprised by defeating Democrat Hillary Clinton in a series of key contests and opening a path to the White House.

US West Texas Intermediate crude futures fell to a session low of $43.07 per barrel, down more than 4% from their last close and their lowest since September, before inching back to $43.26