His spokesman also disclosed that two doctors had been called to Blair's official residence, but that no treatment had been given.
"He (Blair) was not feeling great yesterday evening," the prime minister's official spokesman said.
"My understanding is that a GP (general practitioner) came, and he thought it would be useful to have another opinion. The problem appeared to pass pretty quickly," said the spokesman, who briefed reporters on condition of anonymity.
"Whatever it was it did not require any treatment. The prime minister is perfectly fine and getting on with his job."
The health of the 50-year-old prime minister became a concern a month ago when he was treated at a London hospital for a rapid, irregular heartbeat. An electric jolt was used to return his heart rhythm to normal. His office said then that his health was fine.
"In response to newspaper speculation, a lot of it inaccurate, we can confirm that late this afternoon the prime minister saw a doctor because he was experiencing stomach aches," the spokesman said Wednesday on condition of anonymity. "He was checked over, he is now fine. He is working in his flat and will be chairing Cabinet tomorrow as usual."
The spokesman said Blair was "absolutely fine" and "not ill."