At least 38 girls and young women have been killed in a crash while travelling to a famous traditional festival in Swaziland, a rights group has said.

About 20 others were injured when the truck they were in collided with another vehicle on Friday, the Swaziland Solidarity Network said in a statement.

The young women and girls were allegedly travelling on the back of an open truck, the rights group said.

Police in Swaziland discouraged reporting on the accident, said the group. Photographers were prevented from taking pictures at the scene, said a Swazi journalist.

A high-ranking police officer contacted by The Associated Press refused to comment, saying the matter was related to the “highest authority,” and so no details could be disclosed to the media.

“You don’t hide a death,” said Lucky Lukhele, spokesman for the Swaziland Solidarity Network.

Members of the Swaziland Defence Force alerted the rights group to the accident, Mr Lukhele said, adding that he expected the death toll to rise.

The women were travelling on a motorway between the cities of Mbabane and Manzini when the truck carrying them smashed into another vehicle and was then hit in the rear by a second truck, the Times of Swaziland reported.

“We were about 50 on board the first truck that smashed into the Toyota van,” said Siphelele Sigudla, 18, a survivor quoted by the Times of Swaziland.

The girls and young women were on their way to the Swazi King’s royal residence for the annual reed dance.

About 40,000 participate in the eight-day ceremony in which they sing and dance, often bare-breasted, as they bring reeds to reinforce the windbreak around the royal residence, a government website said.

Swaziland is Africa’s last absolute monarchy, ruled by King Mswati III since 1986.

Swaziland held parliamentary elections in 2013, but many international observers say the electoral process is manipulated to prolong the king’s hold on power.

According to the King, Swaziland’s image has been damaged by misinformation.