An anonymous posting on the website indymedia.ch claimed responsibility for the attack on the Posthotel Morosani, saying it was directed at Swiss government officials and senior executives of Swiss bank UBS staying at the hotel. Its authenticity couldn't immediately be confirmed.
The Swiss federal prosecutors office said in a statement that it is investigating the incident but provided no further information "for tactical reasons."
The explosion happened in a hotel storage room shortly after 9 a.m. local time (0800 GMT) Thursday, regional police spokesman Thomas Hobi told the AP. The hotel did not comment.
The anonymous claim of responsibility said "two pyrotechnical devices and sugar" were used to cause the blast.
The hotel is just over a mile (around 2 kilometers) from the main venue of the annual gathering in the Alpine ski resort.
There was little disruption to the hotel and its activities beyond an increased security presence at the hotel's entrance. Guests, journalists and others were filing through a security scanner that was installed before Thursday's incident.