A huge blast rocked a hotel and office complex occupied by unidentified gunmen in Kenya’s Capital Nairobi on Tuesday. The blast was followed by more explosions, and soon a gun battle erupted between security forces and the attackers, The Guardian reported. The gunfight is still under way.

At least four armed men entered the Dusit Hotel D2 compound around 3 pm local time (5.30 pm Indian Standard Time), the daily quoted witnesses as saying. Automatic fire and explosions were heard soon after. “There was a bomb, there is a lot of gunfire,” an unidentified man working at the hotel compound told AFP. Security officials are now evacuating people from the hotel.

A police spokesperson told The Guardian that the forces initially treated the incident as a robbery. “As of now we are treating it as anything, including the highest attack,” Charles Owino said over phone. “All police teams including anti-terror officers are at the scene.”

The Daily Nation reported that the attackers arrived at the complex in a car, and forced the security guards to let them enter by shooting at them. The gunmen hurled explosives at vehicles in the parking lot before entering the hotel.

The Bomb and Hazardous Disposal Unit has cordoned off the vehicle used by the attackers, and is trying to determine whether it contains explosives. The National Police Service tweeted that the area has been cordoned off and motorists have been asked to use alternative routes. Specialised police units are at the site to engage the attackers, it added.

Terrorist group Shabaab al-Mujahideen, also known as al-Shabaab, has claimed responsibility for the attack, the SITE Intelligence Group reported.