South Africa has closed one of its busiest border crossings with Mozambique following violent post-electoral protests in the neighbouring country.

The protests have led to deadly clashes in several cities following last month's disputed presidential election, won by Mozambique’s ruling Frelimo party.

The authorities say there are reports of vehicles being torched on the Mozambican side of the Lebombo port of entry.

"Due to these security incidents and in the interest of public safety, the port has been temporarily closed until further notice," the South African border agency said.

Lebombo, one of the four busiest land ports in southern Africa, is about 110km (68 miles) from Mozambique’s capital, Maputo, and about 440km from South Africa’s capital of Pretoria.

Travellers have been advised to use alternative crossing points between the two countries.

Violence had spread to Ressano Garcia, a small area in Maputo province, near Lebombo, said Michael Masiapato, South Africa’s Border Management Authority (BMA) commissioner.

Mr Masiapato said the South African side was not affected, but safety measures needed to be taken.

"Some buildings have been set alight. At the moment we are working on securing the Lebombo border as well as travellers’ safety," he said in a statement.

"The border will be closed to ensure the safety of travellers."

Reports say protesters on the Mozambican side of the border have burnt down an immigration office in that country.

Seven Mozambican officials have requested refuge on the South African side for safety and protection, the authorities said.

BMA officials, the South African police and the army have been engaged to stop the protests from spilling over into South Africa.

Demonstrations started at the end of October in Maputo after Daniel Chapo, the Frelimo candidate, was officially declared the winner with more than 71% of the vote.

Opposition leader Venâncio Mondlane, who came second with 20% of the vote, went into hiding before the results were announced.

He cited fears for his safety after his aide and lawyer were killed as they were preparing to challenge the results.

The protests have led to violent clashes with the police and at least 18 people have been killed, according to Human Rights Watch.

The internet and social media have also been restricted.

A general strike called by Mondlane has continued, despite the prime minister's call for people to return to work.

On Tuesday, Defence Minister Cristóvão Chume threatened to deploy the army ahead of nationwide protests called for Thursday.

Chume said the post-election protests were intended "to change the democratically established power".