PORTSMOUTH -- The state medical examiner's office said yesterday that a Portsmouth toddler who was found in a vehicle died from overheating, also known as hyperthermia.

The 2-year-old boy was found unresponsive in the vehicle near his residence Thursday.

Portsmouth police have not identified the boy or provided details about the circumstances of his death. Police spokeswoman Ann Hope said an investigation is continuing.

The death is the first such fatality reported in Virginia this year.

In Henrico County last month, a woman was charged with two counts of felony neglect after an off-duty Richmond police officer pulled two children from the woman's car in a shopping center's parking lot. Police estimated the temperature in the car's interior had reached about 130 degrees. The high that day in the area was 100 degrees. The children, a 4-year-old and an 8-month-old, survived.

The woman, Fredrika Michele Simpson, is the great-aunt of the children. She has a preliminary hearing set for Aug. 25.

Nationally, there have been at least 13 deaths this year of infants and children left inside hot vehicles. There were at least 35 such fatalities in the U.S. last year, 42 in 2006 and 30 in 2005.