(CNN) -- A total of four earthquakes -- the strongest of them a powerful 7.2 magnitude quake -- hit western China on Friday, the U.S. Geological Survey reported.

The Chinese Seismological Network also reported the quakes -- estimating the initial quake at 7.3 on the Richter scale and reporting a fifth tremor about two hours afterward. The network uses the Richter scale to measure quake intensity rather than magnitude.

There were no immediate reports of damage or fatalities, a spokeswoman for the seismological network said. She said the quake happened in Yutian County, a remote region in the Kunlun Mountains far from any residential areas.

The quakes hit the border area of western China's Xinjiang and Xizang regions starting at about 6:30 a.m. local time, according to the USGS. Their epicenters were all at least six miles under the Earth's surface.

The last aftershock hit the area more than an hour later.

The USGS considers earthquakes between 7.0 and 7.9 to be "major" earthquakes.

The temblor was followed about 17 minutes later by a magnitude-5.3 aftershock, according to the USGS. The two that followed were magnitude 5.5 and magnitude 4.8. E-mail to a friend

CNN's Wen-Chun Fan contributed to this report.

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