Gunmen have attacked a Kenyan university during morning prayers today, killing four and injuring at least 40, with the death toll expected to rise.

Masked gunmen stormed the Garissa University College campus near the Somalian border on Thursday morning, around 5.30am local time. A number of students have been taken hostage, and gunfire exchanged with security forces. The gunman have managed to gain entry to the student's accommodation.

A statement from the head of Kenya's police force, Joseph Boinet, said the attackers shot "indiscriminately while inside the university compound". Security officers are now "engaged in an elaborate process of flushing out the gunmen," he added.

A doctor at Garissa hospital told Reuters they had received 49 casualties so far, all with bullet and shrapnel wounds and Kenya's National Disaster Operation Centre said at least four were in critical condition, and four airlifted to Nairobi for treatment.

No group has yet claimed responsibility for the raid, which took place just before dawn. However, Somali Islamist militant group al Shabaab, which has links to Al Qaeda, has in the past carried out attacks in Garissa and in other parts of Kenya. The group claimed responsibility for the September 2013 attack on the Westgate shopping mall in Nairobi which resulted in the deaths of at least 67 people.

Al Shabaab has declared it will punish Kenya for sending troops into Somalia alongside African Union peacekeepers to fight the group.

Grace Kai, a student at the neighboring Garissa Teachers Training College, said there had been warnings that an attack could be imminent.

"Some strangers had been spotted in Garissa town and were suspected to be terrorists," she told Reuters.

"Then on Monday our college principal told us ...that strangers had been spotted in our college... On Tuesday we were released to go home, and our college closed, but the campus remained in session, and now they have been attacked."

The country's president Uhuru Kenyatta reportedly declared just yesterday that ''Kenya is safe.''

Addtional reporting by Reuters