The US Federal Reserve may raise interest rates as soon as June, according to two top officials from the central bank.

The expectations from Loretta Mester, president of the Cleveland Fed, and John Williams, president of the San Francisco Fed, come as many economic experts see the central bank delaying a rate increase until December, given the country's dismal first quarter.

Mester told reporters in Philadelphia that "all meetings are on the table" for the first interest rate rise in nine years.

"We're getting close to the point where it's going to be time to lift off, and now it's going to be this decision based on the data."

"There are a whole bunch of data releases that will come out between now and June. But to me the employment reports will be indicative of a lot," she said.

Agreeing with Mester, Williams told reporters that all meetings are "on the table".

"Really positive data trends, improvement in the labour market, signs that improve the confidence and the expectation that inflation will move back to 2% - I mean could imagine that constellation of data coming in, whether before June or meetings right after that too," Williams said.

"But that would require the data to be good."

The Fed, which has held the main rate near zero since December 2008, earlier said in its latest policy statement that the headwinds that stall growth might fade and the economy would experience moderate growth.

The US economy grew 0.2% year on year in the first quarter, down from a 2.2% rate in the previous three months, due primarily to harsh winter weather and delays at West Coast ports.

Warren Buffett's view

Billionaire investor Warren Buffett earlier said in an interview with CNBC that the Fed will not be in a hurry to raise interest rates given first quarter data and the negative bond yield in Europe.

"I think it would be very hard for the Fed to bump rates up here with negative rates in Europe," the Berkshire Hathaway CEO said.

"Things like autos are very strong; things like housing are a little better. In our rail car holdings, you see that it isn't that strong but on the other hand it's not going backwards at all."