Owners of dry bulk ships and tankers face sharp falls in profitability after rates for the largest ships at least halved since May on fears about ship oversupply and weak global demand.

The fall-off could revive fears about the finances of the weakest companies, some of which are struggling to finance significant orders of new ships.

The average rates paid to charter Capesize ships – the largest dry bulk carriers – on the short-term spot market have fallen from a peak of $60,000 a day in mid-May to $23,012 yesterday.

In the tanker market, rates on some routes for very large crude carriers, the largest commonly used type, were more than $75,000 a day in early June but closed last week at less than $20,000 a day on one route, according to PF Bassoe, an Oslo-based shipbroker.

Chinese demand for iron ore and coal – the key commodities for the dry bulk market – has slackened in recent weeks. Many tankers have finished long-term contracts to store oil. Both markets have also seen significant ship deliveries.

Denis Petropoulos, a director of London-based Braemar Shipping, said the surprise had been how well the tanker market had held up for most of the year. Slower-than-expected deliveries of new vessels and the use of others for oil storage had boosted rates.

Ships were now finally being delivered and storage contracts were ending.

“It has fallen back to levels we expected it to be for most of the year,” Mr Petropoulos said of the market.

Johnny Plumbe, chief executive of London-based ACM Shipping, a shipbroker specialising in tankers, said oil demand remained similar to that in the recent past. However, ships coming out of use as storage had competed unexpectedly hard for cargoes.

“The confidence got driven out of the market slightly,” he said.

On dry bulk, Henriette van Niekerk of London-based Clarkson shipbrokers said there were signs the Chinese government was regulating energy-intensive industries more strictly. Falling steel prices and rising iron ore prices had squeezed margins for many Chinese steelmakers.

“The story's about how they're managing this differential between the contractual price of iron ore and the steel price,” she said.

The falls come little more than a year after many tanker and dry bulk owners were struggling to rearrange their finances in the wake of the 2008 financial crisis. Many are still struggling to pay for expensive ships ordered at the height of the industry's 2001-08 boom. However, any new problems resulting from the rate falls are expected to fall mainly on smaller, weaker dry bulk owners.

Alun Hatfield of Clarkson said owners' problems would depend on what prices they had paid for ships – and rates were also still better than often in recent years. “If you look at the 10-year average time charter rates, $25,000 a day is a pretty good rate.”