A prolonged government shutdown could start to take a toll on the US economy, the Federal Reserve chairman has warned, as the impasse over funding between Donald Trump and congressional Democrats neared the end of its third week. 

At a lunchtime event in Washington, Jay Powell said that past government shutdowns had been fairly shortlived affairs that did not leave much of a mark on the economy. But if the current one lasts too long it could begin to have a noticeable impact, he said.

His words came as the president cited the shutdown in cancelling a trip to Davos, Switzerland that was planned for later this month, in a sign of how entrenched the battle over federal funding has become. Mr Trump on Thursday travelled to Texas to reiterate his demands for congressional funding for a border wall, a key sticking point in talks over the budget.