TOKYO — Japan’s newly installed prime minister startled the nation on Friday by warning that it could face a financial crisis of Greek proportions if it does not tackle its colossal debt.

The stark words from the prime minister, Naoto Kan, followed by just hours the resignation of his banking minister and ally in the governing Democratic Party, Shizuka Kamei — an advocate of big spending. Mr. Kamei’s departure seemed to signal that the new government would focus on reducing Japan’s heavy government debt, called sovereign debt, by far the highest in the industrialized world, and cutting back on the wasteful public works projects.

“It is difficult to sustain a policy that relies too heavily on issuing debt,” Mr. Kan told the Japanese Parliament in his first policy speech. “As we have seen with the financial confusion in the European Community stemming from Greece, our finances could collapse if trust in national bonds is lost and growing national debt is left alone.”

Worried by the Greek debt crisis, policy makers around the world have increasingly raised the alarm over runaway government spending of the past two years, as the world has grappled with an economic crisis.