* "Xaver" halts transport and cuts power lines in Scotland
* Storm kills two in Britain, one in Denmark
* London's Thames Barrier flood defence to close
By Erik Kirschbaum and Belinda Goldsmith
BERLIN/LONDON Dec 5 (Reuters) - Hurricane-force Storm Xaver blasted towards mainland Europe on Thursday after cutting transport and power in northern Britain and killing three people in what meteorologists warned could be the worst storm to hit the continent in years.
British authorities said the Thames Barrier, designed to protect London from flooding during exceptional tides, would shut on Thursday night and warned of "the most serious coastal tidal surge for over 60 years in England". Prime Minister David Cameron called two emergency meetings to discuss strategy.
Two people were killed in Britain as the nation's weather office measured winds of up to 225 km per hour (140 mph) when the storm slammed Scotland and parts of England.
A lorry driver was killed and four people injured when his vehicle overturned and collided with other vehicles in West Lothian, Scotland, police said, while a second man died near Nottingham in central England when he was hit by a falling tree.
In western Denmark the 72-year-old female passenger of a truck died when the vehicle overturned in high winds.
More than 100,000 homes were left without power across Britain, 80,000 of them in Scotland, according to energy company SSE.
North Sea oil and gas producers including ConocoPhillips , Maersk Oil, and Statoil cut production and evacuated staff from some platforms.
All train services in Scotland were cancelled on Thursday morning due to debris on the tracks but services were slowly restored during the day. Lifeboat crews were called to rescue people from flooded homes in Rhyl in north Wales.
Low-lying coastal areas of eastern England were waiting for the storm to hit on Thursday evening, with the Environment Agency issuing 41 severe flood warnings, the highest category.
Police were advising more than 15,000 people to evacuate east coast areas vulnerable to tidal surges, although sea defences have been strengthened since storms and flooding killed hundreds on the North Sea coast in 1953.
HAMBURG ON ALERT
Germany's northern port of Hamburg was preparing for a direct hit, which some forecasters said could be as powerful as a storm and flood in the city in 1962 that killed 315.
Of the 377 planes that had been due to land at or take off from Hamburg airport on Thursday, 120 were cancelled or diverted due to high winds. The airport said it expected further cancellations and delays on Friday.
In Hamburg a fish market was flooded. Many schools and Christmas markets were closed. Ferries to Germany's North Sea islands were kept in port and some industrial plants closed.
"The truly dangerous thing about this storm is that the winds will continue for hours and won't let up," said Andreas Friedrich, a German weather service meteorologist. "The danger of coastal flooding is high."
Friedrich said people were being advised to stay indoors because of the risk of trees being toppled or roofs blown off. An extreme weather warning was issued for the northern states of Hamburg, Schleswig-Holstein, Lower Saxony and Bremen.
The German transport ministry said until Sunday people should limit travel by road and rail to journeys which are "absolutely necessary". Train services were restricted.
The Oresund bridge linking southern Sweden with Denmark was shut at 1500 GMT. Some railway lines in southern Sweden were closed, with high winds expected in the south and heavy snow further north.
In Denmark, railroad company DSB said it would stop operating most trains. Airline Alsie Express cancelled all domestic flights and the 6.8-km (4-mile) Great Belt Bridge, which includes a 1.6-km (1-mile) suspension bridge section, was closed.
Copenhagen Airport, the Nordic region's busiest airport, closed to all traffic on Thursday evening until Friday at 0700 GMT due to the storm.
Trains in the northern Netherlands were halted, Dutch Railways said. At Amsterdam's Schiphol Airport 50 flights were cancelled, a spokeswoman said, adding there could be further cancellations.