The blade sits at the top of a 93-metre-high column
It will not be known until data are gathered from a companion turbine whether high winds in the region are to blame for the breakdown.
The turbine operators, Amec Wind, hope to carry out an investigation with the unit's Danish makers, although bad weather has so far hampered plans for an inspection.
Small boats have been warned to stay away after a blade on one of the two 93-metre-high turbines snapped.
'Not pessimistic'
Dr Chris French, a lecturer in marine electrotechnology at Newcastle University, said it could be a long and tricky job to fix the blade.
Dr French told BBC News Online: "Before there is any attempt to take anything off, they will want to look at some of the data that come back from the instrumented turbine.
"I would also think a huge crane barge will be needed to come alongside to carry out the repair work.
"They are going to have to wait for a suitable gap in the weather before work can start.
"I cannot believe the turbines would have been installed without stress testing being carried out first, so I suspect a materials abnormality.
"These are the first offshore wind turbines of their type in the UK, if not the world, so we should not be too pessimistic about what has happened."
The turbines were opened in December 2000, just under a kilometre off Blyth, in a £4m operation by Hexham company Amec Wind.
The turbines were switched off when the fault was discovered, and an inspection by makers Vestas of Denmark is due on Wednesday.
An Amec spokesman said that although there had been windy weather no cause of the fault had yet been determined.
The turbines, opened by Energy Minister Helen Liddle, can generate enough power for 3,000 homes.