Stocks, sterling and oil soared at the start of the week after polls suggested the U.K. was more likely to vote to remain in the European Union in Thursday's referendum than previously expected.

The Stoxx Europe 600 jumped 3.4% late morning, extending Friday's momentum, while the British pound surged 2.1% against the dollar to $1.4653, on track for its highest settlement since May.

Futures pointed to a 1.3% opening gain for the S&P 500. Changes in futures markets don't necessarily reflect market moves after the opening bell.

"We're in this sort of frenzied period where Brexit is front and center, " said Bob Doll, senior portfolio manager at Nuveen Asset Management.

A survey published on Sunday showed that 45% of respondents backed the U.K. staying in the trade bloc, compared with 42% in favor of leaving. The poll-of-polls, averaging the last six polls in the U.K. vote, returned to 50/50, suggesting growing momentum for the "remain camp" in the June 23 referendum.