Kenya has boosted security a day after suspected Shebab militants from Somalia stormed into a coastal town in a major assault killing at least 49 people, Interior Minister Joseph Ole Lenku said Monday.

"Security has been beefed (up) across the country," Lenku told reporters in Nairobi before leaving for the site of the attack, calling the killings a "heinous act".

Around 50 heavily-armed gunmen drove into the town of Mpeketoni, near the coastal island and popular tourist resort of Lamu, late on Sunday, officials said.

"The red line has been crossed," Lenku said, adding that at least 20 vehicles and several buildings were also torched.

"We must bring to book the perpetrators," he said, calling the attackers "bandits" and saying that security forces had chased them northwards into a remote forest that borders Somalia.

Witnesses said the gunmen first attacked a police station, before starting to randomly shoot at civilians, some of whom had been watching the World Cup in local bars and hotels.

The fierce gun battles continued until after midnight, but by dawn on Monday the town of Mpeketoni was reported calm.

Police spokeswoman Zipporah Mboroki has confirmed that 49 people died, including at least one police officer.