Three major fires, all on the same road, ripped through commercial sites in Gaithersburg and Rockville within a 24-hour period ending last night and caused more than $1 million in damage, Montgomery County fire officials reported.

Officials called the outbreak of fires within three miles "very unusual" and said all are under investigation. No causes had been determined for any of them by late last night, according to county fire and rescue spokeswoman Angela Withers.

The most recent of the blazes was reported about 8:30 p.m. in a vacant building in the 100 block of North Frederick Avenue in Gaithersburg. One firefighter suffered a shoulder sprain in combating the blaze, which was extinguished by about 11 p.m..

About 1 a.m., a blaze gutted a dry cleaners in the Gaithersburg Square shopping center, in the 400 block of the avenue, then spread to three adjacent businesses before being contained by firefighters. A second blaze about two hours later hit a commercial storage facility in Rockville three miles south of the Gaithersburg fire.

The Gaithersburg Square fire originated in the G Square dry cleaning establishment and quickly spread to a Reliable Home Appliances store, a Super Fresh market and Kim's Hunan Restaurant.

Flames gutted the dry cleaning building, Withers said, and the other establishments sustained roof, smoke and equipment damage. Withers said investigators estimated total structural damage at $400,000 and damage to contents at $200,000.

At 2:51 a.m., Withers said, a fire broke out at the Public Storage facility, 16001 Frederick Rd. in Rockville, causing extensive damage to a two-story building that contained rental storage cubicles for household belongings.

Investigators estimated damage at $300,000 to the building and $150,000 to the contents, Withers said. No damage estimate was available for the third fire.