Japan’s bond market has burst back onto the global stage, ending years of uneventful trading with a spike in volatility that is worrying investors already spooked by frictions in US Treasuries.

Investors in Japanese government bonds are bracing for a potential power shift in upper house elections this weekend that could strain the country's already frail finances, with long-dated yields soaring to all-time highs as the vote nears.

The slump in Japan’s long-term bonds intensified Monday, pushing yields sharply higher in a move that puts global debt markets on alert.Most Read from BloombergWhy Did Cars Get So Hard to See Out Of?How German Cities Are Rethinking Women’s Safety — With TaxisAdvocates Fear US Agents Are Using ‘Wellness Checks’ on Children as a Prelude to ArrestsAmid signs of thin liquidity and increasing worries about higher government spending in Japan,