  We report a new measurement of the $e^+e^-\to\Upsilon(nS)\pi^+\pi^-$
($n=1,2,3$) cross sections at energies from 10.52 to 11.02 GeV using data
collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$
collider. We observe a new structure in the energy dependence of the cross
sections; if described by a Breit-Wigner function its mass and width are found
to be $M=(10752.7\pm5.9\,^{+0.7}_{-1.1})\,$MeV/$c^2$ and
$\Gamma=(35.5^{+17.6}_{-11.3}\,^{+3.9}_{-3.3})\,$MeV, where the first error is
statistical and the second is systematic. The global significance of the new
structure including systematic uncertainty is 5.2 standard deviations. We also
find evidence for the $e^+e^-\to\Upsilon(1S)\pi^+\pi^-$ process at the energy
10.52 GeV, which is below the $B\bar{B}$ threshold.
