In a report issued on Monday, the New York-based group described arrests and beatings of opposition supporters, and expressed fear of a new crackdown against protesters.
"The existing climate of intimidation, particularly against the opposition Azadliq bloc, has sent a strong message to voters about whom they should support" in Sunday's balloting, Human Rights Watch said on Tuesday.
"Equally worrisome ... is a real potential for violent confrontation if the opposition decides to attempt large-scale protests after the November elections."
The report did not address several steps ordered last week by President Ilham Aliev in response to allegations that the government would try to rig the election.
He ordered the use of invisible ink and ultraviolet light monitors in polling stations to prevent repeat voting, overruling the protests of many of his aides who said such a method, used recently in Iraq and Afghanistan, was degrading to Azerbaijan.
Aliev also directed that Azerbaijani non-governmental organisations that receive more than 30% of their funding from foreign sources should be allowed to monitor the balloting.
Such organisations had previously been banned from monitoring.
"Equally worrisome ... is a real potential for violent confrontation if the opposition decides to attempt large-scale protests after the November elections"
Human Rights Watch
He also instructed election authorities to ensure that voter lists include voters' addresses.
The moves were praised by opposition groups, but many still warned that the government may try to rig the vote.
Human Rights Watch said that local government authorities interfered brazenly in the campaign, and that the authorities could easily intimidate opposition supporters because about 30% of the work force is in the state's employ.
It said that the government had refused to change the composition of election commissions, currently split three ways between government, opposition and allegedly independent members.
In the past, it said, the commission's makeup "played a central role in facilitating falsification of the vote count."
The group also said that the United States, which has supported reforms to encourage free elections in Azerbaijan, had sent mixed signals about how it would respond in case of fraudulent elections.