A government spokesman said last night that the three-day-long siege, in which the attackers massacred at least 62 shoppers and staff, was close to being declared over.
He said special forces combing the building were no longer encountering any resistance.
"Our special forces are inside the building checking the rooms. We think that everyone, the hostages, have been evacuated, but we don't want to take any chances," Manoah Esipisu said.
"The special forces call this sanitising. At the moment they have not met any resistance, but of course we are not ruling out the possibility that there are a couple of them hiding in a remote room or corner," he added.
After a day of fierce gunfire, huge explosions and black smoke that billowed over the Kenyan capital, the vast centre was quiet 60 hours after the gunmen stormed the complex.
"We're in control of Westgate mall," the interior ministry said in a message on Twitter.
No details on the numbers of hostages released have been given, but 63 people were earlier recorded missing by the Red Cross, a figure thought to include hostages as well as those possibly killed.
Almost 200 were wounded in the attack, and at least 11 Kenyan troops were wounded in intense gun battles yesterday, the army said.
Special forces yesterday also killed at least three gunmen and wounded several in bitter fighting in the part Israeli-owned complex, which was popular with wealthy Kenyans and expatriates. A Kenyan security source and a Western intelligence official said Israeli forces were also involved in operations, along with British and US agents.
Somalia's Al Qaeda-linked Shebab insurgents have claimed the attack, which began midday on Saturday, when the gunmen marched into the complex, firing grenades and automatic weapons and sending panicked shoppers fleeing.
Kenyan army chief Julius Karangi said the gunmen were of different nationalities. Many foreign fighters, including Somalis with dual nationalities, are members of the Shebab force.
"They are from different countries. We have sufficient intelligence this is global terrorism," Karangi said.
Interior Minister Joseph Ole Lenku denied that any of the insurgents were women: "All the terrorists are men," he said, noting: "Some of them had dressed like women."
Police said they had also arrested more than 10 people for questioning.
Kenyan President Uhuru Kenyatta, whose nephew was killed along with his fiancee, called the attack "despicable and beastly."