Attackers set off a bomb and opened fire at a hotel complex in Kenya's capital on Tuesday, leaving at least five people dead.

The attack at Nairobi's Dusit D2 Hotel began around 3:30 p.m. Tuesday afternoon with a huge explosion outside the property. Gunmen then charged onto the grounds and opened fire. 

Witnesses reported seeing at least five bodies at the site of the upscale complex, which includes a hotel, a restaurant, shops and offices. One witness, Duran Farah, told VOA that he saw "many people injured."

Kenyan police chief Joseph Boinnet confirmed there were casualties, but authorities have not released a tally for the dead or wounded.

Boinnett told reporters that police have evacuated many people from the complex and are in the process of securing the property. As night fell, gunfire could still be heard echoing around the site on Nairobi's Riverside Drive.

Police instructed journalists to move back and have cordoned off the area.

Map of Dusit, D2 Hotel in Nairobi Kenya

?Al-Shabab claims responsibility

Somalia-based militant group al-Shabab claimed responsibility for the attack in an online statement. The group later said "fierce clashes" continued at the site and said 47 people had been killed, a number not confirmed by other sources.

The group has carried out several previous attacks in Kenya, including the September 2013 assault on Nairobi's Westgate Mall. That attack claimed the lives of 67 people and injured 150.

The hotel assault comes one day after a Nairobi court said three men accused of aiding the Westgate attack will be put on trial.

Attack started with blast

Witness Duran Farah, who is the former president of Somalia's Olympic Committee, told VOA's Harun Maruf that he and some colleagues were entering the complex at the time of the attack.

"A loud explosion happened at the gate. Next there was shooting, an exchange of fire, a lot of fire, and we see people rushing and running around in every direction," he said. He said he and his colleagues escaped by running down an alleyway.

Workers who escaped the buildings said colleagues had huddled in offices and under desks for safety. 

In response to an inquiry from VOA News, a State Department spokesperson said the U.S. embassy in Nairobi is closely monitoring the attack and working with Kenyan authorities to determine if any U.S. citizens were affected. The spokesperson said all U.S. mission personnel are safe and accounted for.

The State Department says the U.S. embassy "has actively offered assistance to local authorities."

VOA State Department correspondent Nike Ching, Somali service senior editor Harun Maruf, national security correspondent Jeff Seldin, Nairobi bureau chief Daniel Schearf, and reporter Mohammed Yusuf in Nairobi all contributed to this report.