The Thai military has previously said that if they can't dive out, the group may have to wait up to four months for flooding to recede before they can leave.
Food and other supplies are being put in place for that outcome.
Interior Minister Anupong Paojinda later stressed the urgency of the evacuation, adding that rain was forecast "in the next few days", the Bangkok Post reported.
Attempts are being made to reduce the risk of further flooding by pumping water from the cave system, Mr Anupong said.
Water levels have dropped by more than 40cm (15in) since Wednesday, with rescue workers now able to walk through a 1.5km (0.9 mile) stretch from the entrance to what's being called the third chamber.
About 128 million litres of water had been pumped out by Thursday, with the water levels coming down at an average rate of 1.5cm per hour.
The boys, aged between 11 and 16, and their 25-year-old coach went missing on 23 June. It is believed they entered the cave when it was dry and sudden heavy rains blocked the exit.
They were found on a rock shelf about 4km (2.5 miles) from the mouth of the cave on Monday night by two British rescuer divers.
The cave complex is regularly flooded during the rainy season which lasts until September or October.Published: 2018-07-05 14:45:28