Japan's Nikkei share index plunged further on Monday, as US futures pointed to additional losses on Wall Street over President Donald Trump's punishing tariffs.

In early trade in Tokyo, the Nikkei 225 was off 7.35 percent, adding to a 2.75-percent drop on Friday, while in Seoul the Kospi was off 4.8 percent.

Australia's stock index plummeted 6 percent at the open on Monday.

Japanese Prime Minister Shigeru Ishiba said on Monday that the government would continue to ask President Trump to lower tariffs against Japan, but acknowledged results "won't come overnight."

"As such, the government must take all available means" to cushion the economic blow from US tariffs, such as offering funding support for domestic firms and taking measures to protect jobs, Ishiba told parliament.

Ishiba said Trump's decision to slap tariffs on imports from Japan was "extremely disappointing and regrettable," adding that Japan would continue to explain that it had done nothing unfair to the United States.

Ishiba also said he was willing to visit the United States for a meeting with Trump as soon as possible. "But in doing so, we must ready a package of steps on what Japan could do," he added.

Trump's decision to slap a 25 percent levy on auto imports, and a reciprocal 24 percent tariff on other Japanese goods, is expected to deal a huge blow to Japan's export-heavy economy with analysts predicting the higher duties could knock up to 0.8 percent off economic growth. (Agencies)