The attack was reported at about 9:20 p.m. Thursday in the 1700 block of 20th Avenue, at the home of one of the victims, a 76-year-old woman.
Police are still investigating the circumstances of the crime, but Suhr said the suspect apparently believed the woman had "something of value" in the home.
A 56-year-old woman delivering food to the home interrupted the robbery and was also attacked, but was able to flee and get help, according to police.
Both women were hospitalized but are now beginning to recover, Suhr said.
"The good news of the story is, as seriously hurt as the two women were, this won't be a homicide," he said.
The suspect, who attacked the women with a hammer and knife, has not been found, according to police.
He is described as a Cantonese-speaking Asian male who drove off in a beige sedan with triangular rear taillights, Suhr said.
Police are seeking the public's help in solving the case.
"We'd love to get more tips than we've already gotten," Suhr said.
Anyone with information is encouraged to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.
The chief also said San Francisco residents, particularly those in the city's Asian communities, should be wary of any attempts at intimidation, extortion or other crimes during the upcoming Chinese New Year celebrations.
"If they get any inkling that they're getting intimidated, or asked for money, anything that makes them anxious, please contact the Police Department," Suhr said.