A SURGE in passengers from Tseung Kwan O crossing the harbour to Hong Kong Island has filled the tunnels in Quarry Bay MTR station close to capacity and forced the company to take measures to keep crowds in check. But the situation is set to get worse as Tseung Kwan O new town is not even half finished, and more firms are due to move to Quarry Bay, increasing pressure on the station. Deputy operations director of the Mass Transit Railway (MTR), Roger Kynaston, said: ''We are concerned about the place, which is why we have more measures there than at some other stations.'' The choke points are the corridors linking the lower level Kwun Tong Line with the Island Line, where the MTR has recently deployed extra staff and improved signs to try to maintain order. Around 30,000 passengers are now moving through the corridors from the Kwun Tung Line during the morning rush hour, which is starting to approach the station's estimated capacity of 36,000 an hour. The MTR believes most of the increase has come from people moving to Tseung Kwan O, also known as Junk Bay. ''We now have people coming in from Tseung Kwan O, taking the bus to Lam Tin station, then taking the MTR across the harbour,'' said an MTR spokesman. The company is one month into a major investigation of Quarry Bay station to see whether it can cope with the increasing pressure. Among the areas being looked at is the rapid increase in the number of office workers in Quarry Bay, an area targeted by Swire for major development. Dorset House and Hong Kong Telecom Tower are set to open early next year, bringing in an estimated 6,000 extra commuters, nearly all of whom will start work at 9 am and will have to go through the station at its busiest time. Meanwhile, Tseung Kwan O new town will grow steadily from the present 130,000 to 143,000 by 1996. In the following five years many other private developments will come on stream and the population in the area will more than double to 297,600 by 2001. The MTR's survey will look at possible improvements to Quarry Bay station itself and the feasibility of running extra trains on the Island Line to keep the platforms clear. But the survey may recommend that these measures would not be enough and that the Kwun Tong Line should be extended to Tin Hau. ''That has to be an option,'' said an MTR spokesman. New signs at Quarry Bay numbering the corridors 9, 11 and 13 in large letters have made public for the first time the MTR's internal numbering system. The move was a response to potentially disastrous confusion when passengers called up the station's control room on the intercom system to complain of overcrowding or report accidents and were unable to say which corridor they were in. Station staff then had to go through each of the three corridors trying to find the problem, wasting precious seconds. An MTR spokesman said the main restriction at Quarry Bay was the fact that Corridor 9 was much longer than the other two. As a consequence passengers crowded into the other two while 9 was only half full. An extension of the MTR to Tseung Kwan O is included in the Railway Development Plan, but the MTR has said the existing system cannot cope with the increase of passengers that would bring and the extension would have to wait until after the airport railway is finished when the third cross harbour MTR tunnel will increase capacity.