At least four people were killed and scores wounded on Thursday when masked gunmen stormed a university campus near Kenya's border with Somalia, taking students hostage and exchanging fire with security forces over several hours.
Police and soldiers surrounded and sealed off Garissa University College and were attempting to flush out the gunmen, the head of Kenya's police force, Joseph Boinet, said in a statement.
"The attackers shot indiscriminately while inside the university compound," he said.
A policeman at the scene said some students had been taken hostage. "We can't tell how many but they are many since the college was in session."
No group claimed responsibility for the raid, which took place just before dawn.
Somali Islamist militant group al Shabaab, which has links to Al Qaeda, has in the past carried out attacks in Garissa, which lies around 200 kilometres (120 miles) from the Somali border, and in other parts of Kenya.
Most of the wounded had been hit by gunfire and four were in a critical condition, the country's National Disaster Operation Centre said on its Twitter feed. Four had been airlifted to Nairobi for treatment, it said.
"I can tell you that we have 49 casualties so far, all with bullet and (shrapnel) wounds. Four people are dead," said a doctor at Garissa hospital.
Grace Kai, a student at the neighbouring 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."
Al Shabaab, which was responsible for an deadly attack in 2013 on the upscale Westgate shopping mall in Nairobi, has declared it will punish Kenya for sending troops into Somalia alongside African Union peacekeepers to fight the group.