OK Guys - let me say what I had in mind ... you guys can tell me how probable it is.
1. This scenario is only meaningful in the context of a India-Pakistan/ China war, where hostilities are breaking out in multiple fronts. The thrust at the Islands will be essentially aimed at keeping the merchant marine open for PRC - especially oil and raw materials.
2. (If I am in charge of PLAN operations to take Great Nicobar
) The first idea would be to get a supply lien through Burma. It won't be easy - the allies did it in WW-2, called the famous "Burma road". It would be a long winding road through the mountains and jungles of Burma, but it will reach the coast all the way from China. Once this road is established (a lot of work has already been done, by the way), I would push thousands of tonnes of supplies into the PRC built ports in China - pretext, trade and infrastructure development in Burma. The Junta will keep quiet since the PRC is their godfather. I will also secretly build up a significant naval personnel presence in these ports. Remember, you do not need to have destroyers and aircraft carriers to invade a little inhabited island. You need infantry (marines) and engineers and equipment and shallow water vessels to land them. One container ship from PRC, stationed in Burma can be modified to carry several landing crafts for an invasion.
3. The first shots obviously will not be fired in this front. The opening volleys will come through Pakistan in the west, followed by PLA/ PLAAF in the north east. Once India is engaged in these areas, PLAAF will carry out a series of sorties on the eastern shores and the Andaman Islands, probably using missiles and LGBs from their "crappy fighters" like J-7Bs and JH-7s.
4. The Tri-services bases in the islands can be carpet bombed by PLA missiles and PLAAF "suicide" mission fighter/ bombers. A few well targetted missiles can take away the airfields for 2-3 days, which is all they need. As IAF gets engaged in thwarting PLAAF, a PLAN task force will sail from Burma and take over a small area of Great Nicobar island with marines, engineers and hundreds of tonnes of equipment. The PLAN engineers will start assembling shore based guns, SAM batteries and preparing an airfield. With the heavy equipment and engineering skills PLAN will have a working airfield in place in 2-3 days, where a squadron of PLAAF J-10B and PLAN J-15B fighters can be flown over from China/ Burma and stationed. A squadron of PLA attack Helos and a few transport Helos can also be sent over to the island.
4. Now with air cover in place, PLAN can start sending in supply ships, frigates and destroyers from mainland China. PLAN can also station a SSBN/ SSGN in the Great Nicobar island. Once a fleet of ships is in place, PLAN can then start building a naval port/ base in the island, while PLA/ PLAAF can start increasing their aircraft fleet. The first toehold will then become the launching point for PLA assault on the rest of the island.
If you think this is unconvincing, please read about Iwo Jima ...