The tremor, measuring 6.4 on the Richter scale, destroyed dozens of houses when it hit Guyang county, about 540 km (335 miles) north-west of Peking, the State Seismological Bureau said.
"The exact situation is still not clear," said an official. He was unable to confirm a report by China's Xinhua news agency that 33 people had been seriously hurt. An official in Peking said the death toll could climb further. At least 36 people were injured in Baotou city, including one man who broke his spine after jumping out of a window in terror.
The authorities had sent squads of soldiers and doctors around Baotou to treat the injured and assess damage, officials said.
A Seismological Bureau official said strong aftershocks, measuring around five on the Richter scale, were possible in the region, but a tremor stronger than the first was unlikely.
The earthquake was felt as far away as Xi'an city, more than 700 km (435 miles) away. In Peking, the tremor sent tall buildings swaying for about 30 seconds.
Chinese seismologists have said the country is experiencing a high-risk period of earthquake activity. An earthquake measuring 6.1 on the Richter scale rumbled through Inner Mongoliain March, but no casualties were reported.
An earthquake measuring 6.9 on the Richter scale rocked north-western China's Xinjiang region in March, killing 26.
In February, a tremor measuring 7.0 struck Yunnan province in the southwest, killing 304 people in China's deadliest earthquake for several years.