All Chinese illegally entering Hong Kong after midnight Thursday will be sent back to China, said the governor, Sir Murray MacLehose, adding that the British Colony is mobilizing hundreds of troops to prevent them from returning. Tough new measures against immigrants include an end to the "touch base" system, under which Chinese who managed to reach urban areas were allowed to stay. But during a three-day grace period illegal immigrants already here will be given identity cards and allowed to stay. Beginning Monday, all residents must carry identity documents. Anyone without them can be arrested and sent to China.