NAIROBI (AFP) - Gunmen have massacred at least 36 workers at a quarry in a fresh attack in troubled north-east Kenya, police and the Red Cross said on Tuesday, the latest in a series of attacks.

The attackers reportedly sprayed gunfire at tents where the workers were sleeping in the early hours of Tuesday morning near the town of Mandera, where Somalia's Al-Qaeda-affiliated Shebab and other militia have carried out a string of raids, Kenyan media said.

The quarry killings follow a separate attack on Monday night in the town of Wajir - which like Mandera is close to the dangerous border with war-torn Somalia - which left one person dead and 12 wounded when gunmen hurled grenades and fired into a bar.

"Our team is on the ground undertaking assessments of the attack," the Kenya Red Cross said on Tuesday.

Police spokesman Zipporah Mboroki confirmed the attacks but said the force would provide exact tolls of those killed later.

However, a senior police official said 36 people had been killed and there were fears others may have been abducted.

"We have lost 36 people, but there are others missing," said the police official, who asked not to be named. "We don't know whether they were taken by the attackers."

The quarry attack, some 15 km from the remote town of Mandera, is close to where Islamists last month executed 28 non-Muslims who were grabbed from a bus.

The Shehab said the bus attack was carried out in revenge for police raids on mosques in Kenya's key port of Mombasa.

Kenya has suffered a series of attacks since invading Somalia in 2011 to attack the Shebab. Kenyan forces have since joined an African Union force battling the Islamists.

No one has so far claimed responsibility for either of the attacks overnight Monday to Tuesday.

Several key unions including for civil servants have warned members to leave the restive northeast until the government can ensure their safety.

Professionals working in the largely Muslim and ethnic Somali north-eastern regions often come from further south in Kenya, where Christians make up about 80 per cent of the population.

Those working in the quarry attacked on Tuesday were also reported to have been from outside the region.

On Sunday, Kenyan media reported that the embattled interior minister and police chief may soon be sacked over "repeated lapses" in security following a wave of attacks.

Both officials mentioned in the report have been under fire since last year's attack by the Shebab against the Westgate shopping mall in Nairobi, in which at least 67 people were killed in a siege involving just four gunmen and which lasted four days.

Worries over internal security mounted when Shebab rebels massacred 100 people in a string of raids against villages in the Lamu region on the Kenyan coast in June and July.