Democratic presidential candidate Barack Obama on Friday began a week-long vacation with family in Hawaii, pulling back from the campaign trail after a new poll this week showed that nearly half of Americans felt they had been hearing "too much" about Obama lately.

Obama said the unrelenting pace of a historic primary campaign against Hillary Clinton had given him little time to rest, unlike his Republican rival John McCain who wrapped up his party's nomination three months earlier, in March.

But the vacation also comes after a poll by the Pew Research Centre on Wednesday showed that 48 per cent of voters had been "hearing too much about Obama lately."

Only 26 per cent said the same about McCain. "I can imagine that folks need a break from politics ... and they didn't get one," Obama told reporters aboard his campaign plane on Thursday. "My sense is that during the summer months, people are not paying as much attention as in September and October."

The Illinois senator has made headlines through much of the past month with a high-profile trip to Europe and the Middle East, including a speech before 200,000 people in Berlin. McCain's campaign has regularly mocked the attention Obama receives, calling him the "greatest celebrity in the world."

Obama said he would be spending time with his wife and two young children, as well as his grandmother in Hawaii who he had barely seen since launching his White House run nearly 17 months ago.

Obama spent most of his childhood in Hawaii, raised by his mother and grandparents. His father from Kenya left the family when he was 2 years old.