This is a developing story. 

Update as of 7:30 a.m. EDT: Whereabouts of 535 of Garissa University’s 815 students are still not known, Kenya National Disaster Operation Centre said in a tweet posted through its official account.

Security forces are currently working to free an unknown number of hostages believed to be held inside the university campus.

Update as of 5:45 a.m. EDT: Militants of the Somalia-based al Shabab group have reportedly claimed responsibility for the attack on the Garissa University.  

At least 14 people have so far been killed and the death toll is likely to rise, according to media reports. Another 65 people have been injured in the ongoing clashes with the gunmen, who have also taken several people hostage in the university campus. 

According to several media reports, the militants of al Qaeda-affiliated group have released at least 15 Muslim students and are currently holding many Christian students hostage. 

In recent months, Al Shabab has launched several attacks inside Kenya in retaliation to the Kenyan government’s decision to send troops to assist Somalia in its fight against the group.

Update as of 4:00 a.m. EDT: According to the Kenyan Red Cross, at least 30 people have so far been injured in early morning attack on the Garissa University College. While most of those injured were admitted to a hospital in the town, four people with serious injuries were airlifted to Nairobi for treatment, Kenya’s National Disaster Operation Centre said. 

The Kenyan security forces are currently engaged in an “elaborate process” of flushing out the gunmen from the university complex, a senior police official said in a statement.

Update as of 2:00 a.m. EDT: Two university guards have been killed by masked gunmen who attacked Kenya’s Garissa University early on Thursday, according to local media reports. Several students are believed to be trapped inside the campus, located in the town of Garissa, about 230 miles northeast of the capital city of Nairobi. 

“Two guards who were manning the gate at the university have been killed. We can hear gunshots from inside the compound but at this point we can't tell who is shooting at who or what,” a policewoman at the scene of the attack told Reuters.

Original story:

Masked gunmen have stormed a university compound in the eastern Kenyan city of Garissa, according to media reports. Heavy gunfire and explosions have been heard at the Garissa University College and two policemen and a student have reportedly been injured in the attack. The attackers, whose affiliations are not yet known, are believed to be holding several people hostage.

According to local media reports, the university came under attack at 5:30 a.m., local time, (10:30 p.m. EDT Wednesday) on Thursday.

“According to some of the students who escaped, there are around five gunmen and they entered the university dormitory while students were sleeping,” Alinoor Moulid, a freelance journalist based in Garissa, told Al Jazeera. “It is hard to tell [about casualties] because the area is now cordoned off, and it is heavily guarded.”

Although no one has so far claimed responsibility for the attack, the al Qaeda-linked al Shabab group has frequently attacked targets across Kenya in recent years.