Japanese automaker Toyota Motor Corp. said on Thursday it has scaled back production at its San Antonio, Texas, assembly plant as a heatwave strains power supplies in the state.

Texas' power grid operator took emergency measures on Wednesday to avoid rolling blackouts as electricity demand soared.

Toyota may stop production on most days before 2 p.m. and shorten night shifts, effective immediately through mid-August, a spokesperson said.

The plant had scheduled five days of summer shutdown next week, and added two additional days due to a global semiconductor shortage, Toyota said. The seven days of closures are unrelated to the heat wave, the spokesperson added.

Toyota joins a slew of other companies in Texas, including Samsung Electronics Co Ltd, that are using less power as the state enters the fourth day of extreme heat.

"We are carefully monitoring the weather conditions and communicating with local authorities, and will adjust our plans accordingly," Samsung said in a statement on Thursday.

General Motors Co has avoided production cuts at its Arlington, Texas, assembly plant, but has scaled back on air conditioning, the company said on Thursday.

Sources familiar with LyondellBasell plant operations said early Thursday the petrochemical firm reduced power usage at its Houston refinery by switching from electric pumps to steam turbines where possible.

On Wednesday, a LyondellBasell spokesperson said its Texas operations were working on ways "to reduce electricity demand without shutting down assets or compromising the safety and reliability of our operations."

Twice this week The Electric Reliability Council of Texas (ERCOT), the state grid operator, urged residents to cut power use during the hottest hours of the day and warned of a risk for rolling blackouts. Residents were asked to turn up thermostats, defer the use of high-power appliances, and turn off swimming pool pumps.