US trade officials have unveiled plans to impose tariffs of up to 3500 per cent on solar panels from some South-East Asian countries.

It marks a key step towards wrapping up a year-old trade case in which American manufacturers accused Chinese companies of flooding the market with unfairly cheap goods, CNN reports.

The case was brought last year by Korea’s Hanwha Qcells, Arizona-based First Solar Inc and several smaller producers seeking to protect billions of dollars in investments in US solar manufacturing.

The petitioner group, the American Alliance for Solar Manufacturing Trade Committee, accused big Chinese solar panel makers with factories in Malaysia, Cambodia, Thailand and Vietnam of shipping panels priced below their cost of production and of receiving unfair subsidies that make US goods uncompetitive.

For the tariffs to be finalised, the International Trade Commission must vote in June on whether the industry was materially harmed by the dumped and subsidised imports.

The tariffs unveiled on Monday vary widely depending on the company and country but are broadly higher than the preliminary duties announced late last year.

Combined dumping and countervailing duties on Jinko Solar products from Malaysia were among the lowest at 41.56 per cent. Rival Trina Solar’s products from its operations in Thailand face tariffs of 375.19 per cent.

Neither Jinko nor Trina were immediately available for comment.

Products from Cambodia would face duties of more than 3500 per cent because its producers elected not to co-operate with the US probe.

“These are very strong results,” said Tim Brightbill, a lawyer for the US manufacturing group.

“We are confident that they will address the unfair trade practices of the Chinese-owned companies in these four countries, which have been injuring the US solar manufacturing industry for far too long.”

The threat of tariffs on countries that supplied more than $US10 billion ($16 billion) of solar products to the US last year, accounting for the vast majority of domestic supplies, has caused a dramatic shift in the global solar trade.

Imports from the four targeted countries this year are a fraction of what they were a year ago, while shipments of panels from nations like Laos and Indonesia are on the rise.