The mid-afternoon explosion blew out windows and part of the exterior walls on the 19th and 20th floors, and victims suffered cuts, burns and contusions, officials said.
The falling glass and other debris smashed the roofs and hoods of cars on Tverskaya Street, one of the busiest thoroughfares in the city.
The Soviet-era hotel, which caters mostly to foreign tourists, is only a few hundred yards from the walls of the Kremlin and Red Square.
While most of the hotel is devoted to guest rooms, the 20th floor is made up of office space. There are at least 10 offices there, including one belonging to Iosif Kobzon, one of the country's most popular singers who is known as the Frank Sinatra of Russia.
He was not in the office at the time, and it was not clear whether the bomb was intended for anyone in particular.
No one claimed responsibility for the attack. However, feuding Russian businessmen frequently settle their differences with violence, and Russia's top law enforcement officer suggested that might be the cause.
"The situation around the Intourist is very complicated" because of changing property ownership, said Interior Minister Sergei Stepashin. "But I don't call it an act of terror because nobody was killed."
Moscow police were searching the city for four suspects who were believed to have fled in a car, the Interfax news agency reported.