Continue or break the while loop

‘break’ is the right keyword…
code structure below, no custom query needed if used in a standard template.

        <?php

    $posts_per_first_section = 6; //how many posts you want to show in the first section//

    if ( have_posts() ) :
        ?>

        <!-- opening html for first loop -->

        <?php
        /* Start the Loop */
        while ( have_posts() ) :
            the_post();

            //your output per post in the first section//
            //for example//
            get_template_part( 'template-parts/post/content', get_post_format() );

        //check for 'break' out of first loop//
        if( $wp_query->current_post+1 == $posts_per_first_section ) break; 

        endwhile; ?>

        <!-- closing html for first loop -->

        <?php //checking if there are more posts to show in second loop
        if( $wp_query->current_post > 0 && $wp_query->current_post+1 < $wp_query->found_posts ) : ?>

        <!-- opening html for second loop -->

        <?php while ( have_posts() ) :
            the_post();

            //your output per post in the second section//
            //for example//
            get_template_part( 'template-parts/post/content', get_post_format() );

        endwhile; ?>

        <!-- closing html for second loop --> 

        <?php endif; //end checking if there are more posts to show in second loop

    else :

        echo 'no posts found';

    endif;
    ?>