Hong Kong's government on Monday sought to placate concerns about a scheme to allow mainland Chinese visitors to bring their cars into the semi-autonomous southern city.

A day after some 300 people took to the streets to protest against the plan, transport department deputy secretary Patrick Chan said no timetable had been set and described the proposal as "just a trial".

He also responded to safety concerns, saying mainlanders bringing their cars into Hong Kong would have to have local drivers licences.

"Only drivers with valid driving licences in Hong Kong will be considered under phase two of the scheme," he said.

"We will take into account factors including safety and the capacity of road networks before putting phase two into place."

The first stage of the scheme, set to be implemented from March 30, allows Hong Kong drivers to apply to take their vehicles into mainland China. The quota is set at 50 cars a day.

The government said it had yet to set a timetable for the second stage, which would allow drivers from Guangdong province in southern China to bring vehicles into Hong Kong at the same rate.

Protesters on Sunday chanted slogans against the scheme and waved banners that read "No, no, no, mainland Chinese cars" as they gathered in downtown Hong Kong.

One demonstrator, Shirley Cheung, said: "I'm strongly against the plan because Hong Kong drives on the left side of the road, mainland China on the right."

"We have enough traffic accidents as it is, we don't want more," she said.

Tensions between Hong Kongers and mainland Chinese have soared in recent months, fuelled by the increasing numbers of mainland visitors entering the southern city of around seven million people.

A Chinese professor called Hong Kongers "dogs" and "bastards" after a video emerged online showing Hong Kong people scolding a young mainland visitor for eating on a train.

In response, an anonymous group of Hong Kongers published a full-page newspaper advert referring to mainland Chinese and "locusts" and demanding the government stop mainland women from having babies in the territory.