Sparks from electric power lines likely started the blaze that became the most destructive wildfire in Texas history, fire officials said Tuesday.

The Sept. 4 blaze started near Bastrop about 40 kilometres east of Austin, destroying more than 1,500 homes and killing two people.

The Texas Forest Service would not elaborate on the cause Tuesday to The Associated Press. However, a copy of the report obtained by the Austin American-Statesman  stated that the massive blaze started as two fires ignited about eight kilometres apart around the same time.

One fire began when winds toppled a dead pine tree onto power lines, showering the dry vegetation below with sparks. The other fire ignited when fallen tree branches became tangled with power lines, showering dry grass and branches with sparks.

Northerly winds gusted at up to 49 km/h Sept. 4 at the National Weather Service office in Austin, according to the report. The relative humidity was 22 per cent, and temperatures reached 27 C.

The findings echo those of the Bluebonnet Electric Cooperative, the electricity provider for the area, Bluebonnet chief executive Mark Rose said.

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"We, like everyone else, have had investigators in the field attempting to determine the origin and cause of the fires," he told the American-Statesman. "Our investigation also shows that trees blew over and fell into the power lines."

Power was expected to be fully restored in Bastrop County by Sunday, he said.

"Bluebonnet is working hard to safely restore power and remove trees burned during the fire that now pose a danger to our lines if those trees were to fall," he said.  

The Texas Forest Service continues investigating what caused another 283-hectrare blaze in Bastrop County near the main fire, officials said.

Fires 95 per cent contained

The Bastrop County wildfires forced thousands of residents to flee their homes, burned out of control for several days and ultimately blackened more than 80 square kilometres. The fires were 95 per cent contained as of Tuesday, but officials urged residents to clear pine needles and other debris away from their homes to avoid re-igniting some "hot spots."

Texas has been in the midst of one of its worst wildfire outbreaks in state history. A perilous mix of hot temperatures, strong winds and the ongoing historic drought spawned the Bastrop County fires, the largest of the nearly 190 wildfires the Forest Service says erupted in early September.

The Insurance Council of Texas estimates that losses from numerous wildfires in central and East Texas since Labor Day will reach $250 million US. Two other people died in an East Texas fire earlier this month.

Some rain and cooler temperatures in the past week have eased the strain on Texas firefighters, but officials said the fire danger remains high across the state.

The tally of burned homes ranks the Bastrop blaze as one of the nation's most destructive wildfires, many of which have burned in California during the last 20 years. Among them was a series of nearly two dozen fires in Southern California in 2007 that destroyed more than 3,100 homes.

Few were caused by power lines, but those that were caused widespread devastation.

A sycamore limb fell on a San Diego Gas and Electric Co. line to spark one of Southern California's biggest fires in 2007, regulators found. Others were started that year when two SDG&E lines lashed and a Cox Communications cable line struck one of the utility's wires.