It's begun: A rescue operation is officially underway at the Thai cave in which 12 young footballers and their coach are stuck, with 18 divers entering the network at 10am (3pm NZ time).

Thai authorities have just confirmed 13 international divers and five Thai divers are on their way to the group.

The acting Chiang Rai governor told reporters "today is D-Day".

The earliest any members of the group could emerge would be 9pm (2am NZ time).

"Today is the peak of our readiness," said Narongsak Osottanakorn, a former provincial governor who is leading the rescue efforts.

"We will still maintain our planned mission and the two main obstacles are time and water," a spokesperson added.

Medical teams have been rehearsing for three days and are ready to treat the group when they emerge, officials said.

"Assessing the situation now, it is necessary to evacuate the area for the rescue operation," The Guardian reports Mae Sai police commander Komsan Sa-ardluan saying over a loudspeaker at the site.

"Those unrelated to the rescue operation, please evacuate the area immediately."

Row of ambulances heading into Thai cave site - amid reports the rescue is underway or at very least imminent. @abcnews #ThailandCave pic.twitter.com/Cj3qPLZBqk

— Anne Barker (@AnneABarker) July 7, 2018

There has been a flurry of activity at the site today. As well as ambulances that have gathered at the site, American divers have arrived and the nearby relatives' room is empty.

"Officials also announced that during the operation no one is allowed to take photos and if any unsuitable photos come out the person will be held responsible," The Guardian reports.

UPDATE: Thai and int’l divers all heading into briefing now. Rescue most likely today. Once they go in, expect up to 12 hrs of radio silence due to absence of comms. We’ll likely only know when the divers/first boys emerge whether it’s been a success #thamlaungcave #ThaiCave

— Daniel Sutton (@danielsutton10) July 8, 2018