CCTV footage showed a man carrying a rifle fleeing the scene.
Israel's military said it was treating the killings as a terrorist attack.
Both Prime Minister Benjamin Netanyahu and Defense Minister Avigdor Lieberman denounced the attack and said the perpetrator would be brought to justice.
Two Israelis were critically injured and later died of their wounds in the attack that took place in an industrial area near the settlement of Barkan in the central West Bank, according to the Israeli Broadcasting Corporation.
Conricus said the suspect was not known to authorities and was not believed to belong to a Palestinian militant group, saying it appeared to be a "lone wolf" attack. The military said it was investigating whether the shooter deliberately targeted those who were shot. She was moderately wounded and is expected to be released from Beilinson Hospital in the coming days.
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Palestinians work side by side with Israelis in the industrial zone.
Army spokesman Jonathan Conricus called it a "terrorist attack" but added that other unspecified factors were involved.
A manager at another company in the industrial zone, Moshe Lev-Ran, suggested the attack might not have been politically motivated. The worker, who carried a gun, fired back a shot at the gunman, but apparently missed.
The global community regards all Israeli settlements in occupied Palestinian territories to be illegal and a major obstacle to Middle East peace. The settlements are considered illegal under worldwide law, though Israel disputes this.
"Our security forces are chasing after the despicable murderer", Netanyahu wrote on Twitter.
Since last March, at least 191 Palestinians have been killed by Israeli fire, the majority during border protests. It killed more than 2,000 Palestinians in just seven weeks.