A USA Today poll gave Obama 50 percent support among registered voters, compared to 43 percent for his Republican rival.
And a CBS poll put Obama on 48 percent to 40 percent for McCain who is due to be formally nominated this week as the Republican party’s presidential candidate for the November 4 elections.
Obama’s leads were significantly higher than polls taken before the convention. In a USA Today poll taken between August 21-23, the Illinois senator held a four-point lead.
And before the Democratic convention which ended with a spectacular finale when Obama addressed some 80,000 people in a Denver football stadium, CBS had only put Obama three points ahead in the polls.
CBS stressed that 71 percent of those surveyed said they were among the 38 million people who watched Obama’s speech on television.
The Republicans opened their convention in the city of St Paul, Minnesota, on Monday, but have sharply cut back on the usual pomp and ceremony out of respect to those in the path of Hurricane Gustav.
The category two storm, which struck Louisiana early on Monday, comes almost three years to the day since Hurricane Katrina obliterated swathes of the southern state and swamped 80 percent of New Orleans.
Republican President George W. Bush was severely criticised for his administration’s poor handling of Katrina, and a new storm raises painful memories of the catastrophe.
With most media attention focused on Hurricane Gustav, the Republican convention was all but blown off the television screens here, robbing McCain of precious primetime coverage to press home his message to voters.
The CBS poll also said Obama was gaining among independent voters, overturning McCain’s previous 12 point lead to storm six points ahead with 43 to 37 percent.
Obama was also attracting more women supporters, with 50 percent to McCain’s 36 percent. And 67 percent of Obama supporters said they were excited by their candidate, compared to only 25 percent of McCain backers.
The poll, carried out between August 29-31 among 875 people, has a margin of error of some three percent.
However, a CNN poll released late pm Sunday gave Obama only a one percent lead over McCain, standing 49 to 48 percent. The previous CNN poll had the two candidates running in a dead heat. Reuters