LONDON, Sept. 23 (Reuters) - The Baltic Exchange's main sea freight index , which tracks rates to ship dry commodities, hit a fresh four-month low on Tuesday with a slowdown in Chinese demand hurting sentiment.

The index, which gauges the cost of shipping resources including iron ore, cement, grain, coal and fertilizer, fell 3.11 percent or 72 points to 2,246 points, recording its eighth straight fall and was at its lowest since May 11.

''The story over the last week or two has been that demand for the bigger ships has suffered,'' Peter Norfolk, director of consultancy & research at SSY said.

''There has been an apparent slowdown in China's iron ore import demand and a bit less coal imports.''

In recent months Chinese demand for iron ore -- the primary material in the manufacture of steel -- has dominated freight market activity while also adding to swings on the main index.

China's commodity imports slowed rapidly in August as local demand began to look sated after months of Beijing's largesse.

''It is going to need more stimulus from demand to counter the slide,'' Norfolk said referring to the main index.

Port congestion in China as well as off Australia had previously tied up a large number of Capesize vessels, typically hauling 150,000 tonne cargoes such as iron ore and coal. But queues off China have eased, taking its toll on Capesize rates.

The Baltic's Capesize index dropped 7.19 percent or 208 points on Tuesday and was at its lowest since May 6. Average Capesize earnings fell to $23,762 on Tuesday and are 74 percent down since their June peak this year.

''With the Capes in particular the congestion levels are a lot lower off China than they were a couple of months ago,'' Norfolk said. ''That has effectively released a lot of ships back into the market.''

The Panamax index of smaller sized ships fell 1.32 percent on Tuesday, although brokers said there was still Far Eastern demand for soybeans and grains from the United States, which helped drive gains last week.