Seven Laotian villagers entered the cave in central Xaysomboun province, about 125 kilometres (78 miles) northeast of the capital Vientiane, on May 20, state-run Laophattana News said.
They were searching for gold but were trapped inside the cave after heavy rain triggered flash flooding, blocking their exit, it added.
Authorities and villagers have been working to pump water out of the cave, but rescue teams have not been able to reach the group.
“We still do not know whether there are any signs of life or if they are still alive,” Bounkham Luanglat, president of a Laotian volunteer rescue association, told AFP.
About 100 people from Laos and Thailand have gone to the site in Long Chanh district to help in the rescue operations, the association said.
Two Thai rescue specialists and another expert from Finland who participated in the rescue of the “Wild Boars” team - who spent nearly three weeks trapped by flash floods in northern Thailand’s Tham Luang cave complex in 2018 - arrived at the Laos cave yesterday, Laophattana News said.
The Laotian rescue group said in a letter dated Saturday that it was appealing to charities in Thailand for specialist personnel and equipment, including water pumps, generators and thermal imaging devices, to help locate and extract the seven trapped people.
The group described the situation as a humanitarian emergency and urged Thai partners to contribute, as rescuers were working in difficult flood conditions.
“The mission is tough because of rain when we went down (into the cave). We had to move out as the water level was increasing,” Thai rescuer Chakkit Taengtan said in a video posted to his Facebook page on Sunday.
The cave system, located in a remote area, extends deep underground, with multiple levels and some passages reaching more than 100 metres (yards) from the entrance, the Laotian rescue group said.