A bus that plunged into a ravine, killing 37 in Malaysia's worst-ever road accident, was overloaded according to reports Thursday that indicated the vehicle had been banned from the roads and that foreigners were among the casualties.

Authorities say the express bus was carrying 53 people when it veered off a busy and treacherous mountain road Wednesday, tumbling into a deep gully and scattering dead and injured on the mountainside.

Sixteen survivors have been sent to hospitals, with some reportedly in critical condition.

Malaysian media said Chinese, Indonesian, Bangladeshi and Thai nationals were believed to be among the dead and injured.

Staff at Hospital Kuala Lumpur told AFP that one Korean and one Canadian national were among the dead brought there, but authorities have yet to provide a full breakdown.

Housing and Urban Wellbeing Minister Abdul Rahman Dahlan was quoted as saying the vehicle's capacity was 44.

"You do the math," Rahman told reporters when asked if the bus was overloaded.

The bus plied an express line bringing visitors to the Genting Highlands resort, a mountaintop gambling and entertainment park about an hour's drive from the capital Kuala Lumpur.

The vehicle had been blacklisted by authorities, according to leading daily The Star, but the reasons were not stated and AFP could not immediately verify the claim.

A horrific scene greeted rescue personnel as they tried to pull survivors out of the mangled bus, hindered by the sheer 70-metre (200-foot) hillside which the bus had plunged down.

"The operation is finished. Last night we searched for more victims but found none, so we closed the operation late last night," fire department official Christopher Chong said.

Authorities speculated that the driver lost control on a tight bend but cautioned that investigations were still underway.

The tragedy is certain to bring new scrutiny to the issue of safety on the route leading to the resort, which is popular with both Malaysians and foreigners.

The resort's casino and a theme park draw about 20 million visitors per year. It is undergoing a major refurbishment, aimed at bringing in still more visitors, which will see a Twentieth Century Fox theme park open in 2016.

The resort is operated by Resorts World Genting, which is owned by Genting Malaysia, one of the country's largest companies.

Resorts World Genting expressed "sadness" over the accident, but stressed in a statement that it does not operate the bus line.

The Genting Highlands road is notoriously steep and winding and has seen several accidents in recent years, some fatal.

Two Indian tourists died and 22 other people were hurt when their bus overturned in the area last year. Seventeen people died in 1996 when a bus veered off the steep road.