BERLIN, Nov. 12, 1989 (UPI) -- The mayors of East and West Berlin officially opened a new border checkpoint Sunday in what was once the heart of the city, and troops with automatic rifles were later rushed to the site as hundreds of West Berliners surged forward shouting, ''Let us in, let us in.''
The incident came as West German authorities braced for another invasion similar to the one Saturday, which brought an estimated 1.3 million East Germans into West Germany. East Germany said that frontier posts had issued 3,377,029 temporary visas between Thursday and 8 a.m. Sunday.
At the Helmstedt border crossing between the two Germanys, cars on the eastern side were backed up for a staggering 37 miles, with East Germans waiting as long as 16 hours to get across even for a brief visit.
West Berlin Mayor Walter Momper and his East Berlin counterpart Erhard Krack shook hands in Potsdamer Platz in a symbolic act of reunion after East German workers opened a hole in the wall overnight to install a new border crossing station. Potsdamer Platz was the hub of the city before World War II.
''This is historic,'' said Momper, who was attending the opening for the fifth new crossing point since Thursday. ''Potsdamer Platz was once the heart of old Berlin. Now it will beat again as it did before. The traffic will again be flowing.''
Hundreds of West Berliners later surged toward the area chanting, ''Let us in, let us in.'' With the situation threatening to get out of control and the West Berlin police unable to restrain the crowd, East German border troops were ordered to take up positions along a 250-yard stretch of the wall.
Other troops linked arms in a vain bid to push the West Berliners back. Trapped in the middle of the crowd were hundreds of people from West Berlin who were trying to get across to East Berlin. They had valid entry permits and wanted to visit friends and relatives on the other side.
The crowd repeatedly chanted ''open up the border. We want breakfast on the Alex,'' a reference to the Alexander Platz in East Berlin, which is studded with restaurants and shops. Wildly enthusiastic, they broke through West Berlin police cordons and surged through the gap in the wall which had been punched overnight onto East Berlin territory.
As a result, thousands of East Berliners waiting patiently on the far side to visit West Berlin were unable to start filing through to the West. It took 45 minutes before authorities restored order and ended the threat of a West Berlin invasion of their state border.
The East and West German border officials jointly forced a way through the crowd, a lane was opened up and after a lengthy delay the thousands of East Berliners started coming across the border. West Berliners were then also allowed to head the opposite way into East Berlin.
''It's been chaotic here, but now things are under way,'' said Juergen Wohlrabe, West Berlin's parliamentary president. ''It's unbelievable, enormous, when you think three months ago, even six weeks ago, there was no idea we would get this. I have just said hello to the first man to pass the border. He was a Mr. Kraft from East Berlin and he was very happy to be seeing our side of the city for the first time.''
Wohlrabe said Potsdamer Platz evoked many memories for older Berliners. Before the war, it was the capital's busiest traffic intersection and shopping center, but today it is a strip of barren land forming part of the fortified Berlin Wall area.