"This is a very, very good set of results for the Conservatives," said Mr Cameron, who is visiting a wildlife park with his family near his Oxfordshire constituency.
"We have really broken through in the North. We have many more councillors now than people expected."
Labour ministers were, meanwhile, trying to put a brave face on the results, with Ms Hewitt insisting it was not the "complete meltdown" predicted by some.
But she acknowledged that losing so many councillors was a "huge disappointment".
She dismissed Mr Cameron's claim that the Tories were now "the party of the whole country" as "complete rubbish", and urged Labour to unite around Mr Brown.
Ms Hewitt told Sky News: "They weren't as bad as we feared, but they weren't as good as we would like.
"I think there's a real chance now from this mid-term result to build out - with a new leader of course - build on the achievements of the last 10 years, renew ourselves in government, but do so by listening very carefully to what people have told us in different parts of the UK in these results."
Sir Menzies Campbell's leadership of the Liberal Democrat party has, meanwhile, come under fresh scrutiny after his party lost 246 council seats and relinquished control of four town halls to the Conservatives.
Lib Dem chief of staff Ed Davey denied questions were being asked within the party about Sir Menzies' position, claiming it had performed as well as expected.
"I think if you look at our vote share this time which looks like it's more or less neck-and-neck with Labour - 26%.
"It is one of the better results that we've actually had over the last 15 years in local government elections and yes, we've suffered some losses in England but if you look at the seats that we need to gain at the general election we've actually made progress even against the Conservatives in places like Eastbourne."
In Scotland, the SNP took 47 seats, against Labour's 46, and claimed Labour had lost the "moral authority to govern".
The SNP is thought likely to seek a coalition with the Liberal Democrats and Greens - although its pledge for a referendum on independence could prove a sticking point.