By Josie Cox 

European shares tentatively tracked gains on Wall Street on Thursday, but all eyes rested on the Scottish referendum, keeping moves in both currency and stock markets range-bound.

In early trade, the Stoxx Europe 600 added 0.3%, while Germany's DAX and France's CAC rose 0.4% and 0.2% respectively. On Wednesday, the Dow Jones Industrial Average struck yet another record closing high, as investors embraced reassurance from the Federal Reserve that it would continue on its cautious course toward a rate hike next year.

The dollar surged to a six-year high against Japan's yen, hitting Yen108.87, while the euro fell to a 14-month low of $1.2852 before recovering slightly, underscoring the diverging paths between the Fed and the Japanese and European Central Bank, which are both still loosening monetary policy.

Also on Thursday, the Swiss National Bank said it was keeping rates on hold, surprising a minority that had speculated the bank would move lower, driven by its nearly three-year-old policy to keep the euro above 1.20 against the franc.

Switzerland's central bank introduced the minimum exchange rate in September 2011, at a time when an apparently relentless slide in the then crisis-struck euro was threatening to stir up deflation in Switzerland by slamming import prices and pinching exporters.

It hasn't intervened to defend the currency since late 2012, analysts said, but it frequently reiterates its commitment to the exchange-rate floor.

After the announcement, the franc was trading 0.2% higher against the euro at 1.2080 francs.

Scotland assumed center stage as residents started taking to the polls in a vote on whether the country will separate from the remainder of the U.K., ending a 300-year union.

Turnout is forecast to be high, with voting officials expecting more than four million Scots to vote at 2,600 locations across the country.

Pollster YouGov released a survey on Thursday morning that put pro-union support narrowly in the lead. The survey showed 49% of the more than 3,000 people polled between Monday and Wednesday supported keeping Scotland in the union and 45% supported independence. The rest were undecided or didn't know, YouGov said.

"Bookmaker exchanges currently price the 'yes' probability a little above 20%," Josh O'Byrne, a currency strategist at Citigroup says.

"This seems reasonably fair compared to our estimate, although it could be sensible to assume it somewhat higher given the degree of dispersion in the polls," he adds.

The British pound climbed by around 3% during the first six months of the year, hitting a 2014 high of $1.71 against the dollar in mid-July helped by the U.K. enjoying one of the most robust recoveries of all European economies after the financial crisis.

In August however, as the first polls emerged showing that the Scottish vote would likely be close, the currency sold off with investors unsure of what impact a split might have.

On Thursday morning, it was trading marginally higher against the dollar at $1.627.

Geoffrey Yu, a senior currency strategist at UBS said that the results should "create an inordinate amount of intraday [currency] volatility during the Asian session, owing to the fact that results will be drip-fed to the market in parcels."

In the government bond market, the yield on the 10-year U.K. Gilt was at 2.55%, around 0.02 percentage point higher. Yields rise as bond prices fall.

London's FTSE clung to a 0.1% gain in early trade, having closed lower for a third consecutive session on Wednesday.

In commodities markets, gold was 0.9% lower on the day at $1,224.50 a troy ounce. Brent Crude waned 0.6% to $98.36 a barrel.

Write to Josie Cox at josie.cox@wsj.com