Lebanon has enforced new immigration controls at the Syrian border in a move to gain control of the steady stream of refugees from its much larger neighbour.

Shopkeepers and taxi drivers on the Lebanon side of the Masnaa border crossing said thousands of Syrians crossed the frontier yesterday before the rules were implemented at midnight.

A senior security official said on Saturday that Syrians would have to apply for entry permits for the first time and provide information about the purpose and length of their stay.

Lebanon, whose population is less than five million, hosts more than one million Syrian refugees.

It has the highest per capita concentration of refugees in the world.

The government already started restricting refugees late last year.

It is also home to thousands of working Syrians, many of them employed in shops or as labourers.

Resentment among the Lebanese population has spilled over into attacks on Syrians.

Syrians will now have to apply for one of six types of entry permit - tourist, business, student, transit, medical or short-stay.

Each permit requires specific documentation, such as hotel bookings and $1,000 for tourists or an invitation from a Lebanese company for business people.

The United Nations refugee agency UNHCR called on the government to clarify the role of refugees under the new legislation.

"Our concern is that there is no mention of refugees in these new regulations," said spokesman Ron Redmond.

"We'd like some information on exactly how the procedure will be carried out to ensure the most vulnerable can still get in."