Buses caused havoc in the Pretoria CBD on Monday morning as some City of Tshwane employees went on strike demanding 18% salary increases.

The South African Municipal Workers’ Union's Greater Tshwane Region branch said in a statement on Sunday announcing the strike that they also want the city to stop outsourcing services.

Buses blocked off roads, slowing traffic to a snail's pace as motorists made their way into the CBD.

Tshwane Metro Police spokesperson Isaac Mahamba said the drivers parked the buses on big intersections around the city centre and left. He said they were now trying to get spare keys in order to remove the buses.

"Remember they parked the buses and left so we're trying to check if they can give us spare keys," said Mahamba.

"These are city buses, they work for the city so we're engaging with the city for the spare keys."

Mahamba said the "whole CBD" was congested and motorists found it difficult to either enter or leave the city centre.

He said anyone hoping to get to Pretoria CBD must just "forget it".

Samwu met with local corporate and shared services MMC Richard Moheta on Friday.

"If money is good for senior managers, equally we also deserve money. Our demand remains 18% backdated to July 1 2017. As much as we will ensure that an amicable solution is realised soon, our legal team has been instructed to lodge necessary documents with the SALGBC (South African Local Government Bargaining Council) on July 29 2019," Samwu regional secretary Mpho Tladinyane said in a statement on Sunday.

- Additional reporting by Kgothatso Madisa