A number of civilians are still feared to be trapped in a luxury hotel complex in Nairobi with an attack by suspected militants apparently ongoing.
Gunmen attacked the compound in the Westlands district of Kenya's capital on Tuesday, killing at least 15 people.
Gunfire and explosions were heard early on Wednesday and a security operation continues. Civilians have been texting relatives and asking for medical help.
The Somalia-based militant group al-Shabab said it was behind the attack.
The complex houses the DusitD2 hotel as well as offices.
Police sources said 15 people had been killed - reportedly including a British citizen - but an official number has not yet been confirmed by the government.
A US citizen is among the dead, the US State Department said. The fate of the attackers is also unclear.
How did the attack unfold?
The attack began at about 15:00 local time (12:00 GMT) when four gunmen threw bombs at vehicles in the car park before entering the lobby, where one blew himself up, police say.
A woman working in a neighbouring building told Reuters news agency: "I just started hearing gunshots, and then started seeing people running away raising their hands up and some were entering the bank to hide for their lives."
Security camera footage showed at least four heavily armed men walking in and opening fire. There are reports they had been seen visiting the compound in recent days.
At 23:00, Interior Cabinet Secretary Fred Matiang'i said all the buildings in the complex had been secured by security forces.
"The situation is under control and the country is safe," he told reporters. "Terrorism will never defeat us."
But just an hour later gunfire and sporadic explosions were reported in the area. There was more heavy gunfire at about 07:00.
Security forces have been combing their way through the building where frightened workers had barricaded themselves inside. hiding under tables and chairs and in bathrooms.
In the early hours of Wednesday, more than 100 people were rescued. About 30 people are being treated at Nairobi hospitals, media reports say.
The Daily Nation newspaper reported that security forces were advancing on the seventh floor, where people are still thought to be hiding and where the attackers are also believed to be holed up.
The five-star DusitD2 hotel has 101 rooms. Located in the Westlands suburb, minutes from the capital's business district, it has its own spa and several restaurants.
Kenya has seen a number of terror attacks in recent years - most notably in areas close to the Somali border and in the country's capital.
Who are al-Shabab?
They are a militant Islamist group that opposes the Somali government but has also carried out attacks throughout East Africa.
Kenya is part of a regional peacekeeping operation that supports the Somali government in its battle against al-Shabab.
In September 2013, al-Shabab gunmen entered the Westgate shopping mall in Nairobi and targeted shoppers.
During an 80-hour siege at the upscale centre, 67 people were killed.
Two years later, the group carried out its deadliest ever assault in Kenya, shooting dead almost 150 people at Garissa University.