U.S. stocks traded sharply higher in the morning session Thursday as investors bet the U.K. will vote to remain in the European Union in the closely watched Britain's Brexit referendum.

By midday, the Dow Jones Industrial Average added 185.62 points, or 1.04 percent, to 17,966.45. The S&P 500 gained 21.50 points, or 1.03 percent, to 2,106.95. The Nasdaq Composite Index leapt 59.18 points, or 1.22 percent, to 4,892.50.

Voters have been going to polling stations Thursday to cast their votes to decide whether Britain will stay in or leave the European Union, as downpours hit London and southeast England.

The ballot counting will start as soon as the polls close at 10 p.m. local time (2100 GMT). A total of 382 counting areas will be set up, with 380 located in England, Wales and Scotland, one in Northern Ireland and one in Gibraltar.

The outcome is expected to be officially declared at the Manchester Town Hall in the early hours of Friday.

According to six main opinion polls from June 18 to 22, the "Leave" camp was tied with the "Remain" camp.

On the economic front, in the week ending June 18, the advance figure for seasonally adjusted initial claims decreased 18,000 from the previous week's unrevised level to 259,000, below market consensus, the U.S. Labor Department reported Thursday.

U.S. sales of new single-family houses in May 2016 were at a seasonally adjusted annual rate of 551,000, missing market estimates, said the Commerce Department Thursday. This is 6.0 percent below the revised April rate of 586,000.

On Wednesday, U.S. stocks reversed early gains to end lower, as Wall Street assessed U.S. Federal Reserve Chair Janet Yellen's comments ahead of the Brexit vote.