A report showing a forecast-beating rise in April wholesale prices was offset by a downward revision for the previous month, while analysts said a deeper look at the figures suggested the Federal Reserve's preferred gauge of inflation could ease further.

Investors were also digesting a warning from the central bank's boss that the battle against prices was proving tougher than expected and indicated interest rates could remain elevated for some time.

There was also some nervousness on trading floors after Beijing hit out at Washington's decision to impose steep tariff hikes on Chinese imports such as electric vehicles and semiconductors.

The commerce ministry said the decision would "severely affect the atmosphere for bilateral cooperation".

But all focus is on the release later Wednesday of the consumer price index (CPI), which will likely play a key role in the Fed's decision on when to start cutting interest rates, if at all this year.

The report follows readings that came in above expectations in the first three months of the year, denting hopes for a reduction in borrowing costs.

However, the data is forecast to show prices slowing down again.

"Investors are expecting inflation to fall in April," Ameriprise's Anthony Saglimbene said.

"Even if the decline is slight, markets are looking for further evidence that the downward trend in inflation remains intact and, importantly, is not in the process of reversing course higher."

A sense of optimism on Wall Street pushed all three main indexes higher, with the Nasdaq hitting a new record and the S&P 500 coming within a whisker of its own all-time peak.

Asia was mixed, with Tokyo, Sydney, Taipei and Jakarta rising but Shanghai, Singapore, Wellington and Manila falling.

Hong Kong and Seoul were closed for holidays.

The CPI release comes after Fed chief Jerome Powell said readings at the start of the year had lowered his level of confidence that price rises would slow back down towards officials' long-term target. 

"The first quarter in the United States was notable for its lack of further progress on inflation," he said. "We did not expect this to be a smooth road, but these were higher than I think anybody expected.

"And so what that has told us is we'll need to be patient and let restrictive policy do its work."

However, he added that he did not expect the Fed would need to hike rates. 

Also Tuesday, Kansas City Fed chief Jeffrey Schmid warned rates could stay high "for some time" and that he was "prepared to be patient as this process plays out".