Early polls show Hillary Clinton won second debate
US Democratic presidential nominee Hillary Clinton and Republican nominee Donald Trump participate in a town hall debate at Washington University in St. Louis, Missouri, on October 9, 2016 (AFP Photo/Rick Wilking)

Polls suggest that Hillary Clinton won Sunday's bitter US presidential debate against Republican rival Donald Trump as he struggles to shake off a wave of criticism over lewd remarks about women.

But the snap surveys of debate watchers showed a less decisive victory for the Democratic candidate than when the two presidential hopefuls first went head-to-head last month.

A CNN/ORC poll of viewers gave Clinton a clear win in St Louis on Sunday, with 57 percent saying she won as opposed to 34 percent for Trump.

But a YouGov survey showed a narrower victory, with 47 percent of registered voters who watched the debate saying she prevailed and 42 percent saying Donald Trump did. The rest said it was a tie.

Viewers had been more in agreement at the last debate that the former first lady and ex-Secretary of State had emerged victorious, when 62 percent of those surveyed for CNN/ORC said she won.

Expectations were low for Trump, who is under fire for recorded remarks in which he speaks of groping women and using his celebrity status to make them have sex with them.