United States President Barack Obama has formally welcomed Tim Groser as New Zealand's Ambassador to the United States.

In a ceremony at the White House, former Trade Minister Groser presented his credentials to the President in the Oval Office.

Mr Groser replaces former Prime Minister Mike Moore, who left the embassy post last month.

Mr Moore, who has also been director-general of the World Trade Organisation, had what was described as a "minor stroke" in April last year.