The Dow Jones Industrial Average, the most famous equity index benchmark on Wall Street, shot above 20,000 for the first time.

The blue-chip stocks index quickly blew through the much-anticipated milestone in the opening seconds of trading on Wednesday and continued to gain as the morning progressed.

The new record is the culmination of a US rally that started following US President Donald Trump's election, in anticipation he will produce pro-growth policies, but which had stalled in the weeks leading up to the inauguration.

The president's signing of numerous executive orders since his inauguration last Friday has reignited a rally that began after his election victory in November.

Trump marked the milestone with a tweet: "Great!#Dow20K."

Investors said crossing the Dow 20,000 mark was just a number, but still nice to have.

"There are no magic numbers but we like to pretend that there are," said Brian Jacobsen, chief portfolio strategist at Wells Fargo Asset Management in Menomonee Falls, Wisconsin.

The occasion was "like watching your odometer cross over 100,000, or peeking up at the clock and noticing that it's exactly noon", he said.

Thomas Roth, head of US Treasury Trading at MUFG Securities in New York, said the milestone reflects a belief that the pledge to cut taxes and regulation while stimulating the economy will be more business-friendly and increase profits.

"While the Dow hitting 20,000 is one of the least meaningful data points on my screen, it does suggest that the equity rally is pretty broad-based," said Michael Purves, chief global strategist at Weeden & Co in New York.

The Dow came within a point of 20,000 on January 6 as investors banked on pro-growth policies and tax cuts from the new Trump administration.