Flames tore through the World Trade Building in downtown Yan'an in Shaanxi province for some 10 hours, the Xinhua news agency reported.
Seventeen of the injured, aged seven to 51, were guests of a hotel occupying the upper floors of the building, while the other three were staff members, Xinhua said.
They had suffered burns and carbon monoxide poisoning and all were in a stable condition after receiving treatment.
A security guard who helped evacuate guests was still missing, Xinhua quoted an officer with the city's fire department as saying.
A total of about 1,700 residents living next to the building were evacuated.
More than 460 firefighters had brought the blaze under control after noon, the report added. The fire's cause was under investigation.