An intense effort to free a container ship blocking the Suez canal is struggling with strong tides and winds, according to the Egyptian head of the effort, who said he still hoped to free the vessel within days.

The longer the skyscraper-sized Ever Given remains in place, the greater the possibility its load will need to be lightened using cranes, the Suez Canal Authority chief, Osama Rabie, told a press conference on Saturday, a strategy that experts have said would probably extend the salvage effort by weeks.

The megaship, which is as long as New York’s Empire State Building is high, has been wedged diagonally across the canal since Tuesday, blocking one of the world’s most vital waterways in both directions.

Rabie said more than 300 vessels are now treading water at either end of the canal, which links the Mediterranean and the Red Sea.

Addressing journalists in Suez, Rabie outlined Egypt’s efforts with tugboats and excavators to free the bow and propellers of the megaship in order to reopen the canal.

Asked when the ship could be afloat again, he suggested it was possible “today or tomorrow, depending on the ship’s responsiveness to the tides”.

Rabie noted that at 10.30pm on Friday the propellers had been able to spin, although not at full speed.

However, they were jammed again due to the changing tide, he said, adding that rescuers had to resort to excavators again overnight to continue the dredging process.

“The type of soil we’re dealing with is very difficult to manage, as are the tides, which affect the vessel due to its size and its cargo load,” he added.

Peter Berdowski, the CEO of Boskalis, the salvage firm hired to extract the Ever Given, said the company hoped to pull the container ship free within days using a combination of heavy tugboats, dredging and high tides.

He told the Dutch current affairs show Nieuwsuur on Friday night that the front of the ship was stuck in sandy clay, but the rear “has not been completely pushed into the clay and that is positive because you can use the rear end to pull it free.”

Berdowski said two large tugboats were on their way to the canal and are expected to arrive over the weekend. He said the company aims to harness the power of the tugs, dredging and tides, which he said are expected to be up to 50 cm (20 inches) higher on Saturday.

“The combination of the [tug] boats we will have there, more ground dredged away and the high tide, we hope that will be enough to get the ship free somewhere early next week,” he said.

If that doesn’t work, the company will remove hundreds of containers from the front of the ship to lighten it, and by doing so lifting the ship to make it easier to pull free, Berdowski said.

A crane was already on its way that can lift the containers off the ship, he said.

In contrast to earlier claims that strong winds were primarily responsible for the stranding, Rabie said on Saturday they were no longer the key culprits.

“Strong winds and weather factors were not the main reasons for the ship’s grounding, there may have been technical or human errors,” he said. “All of these factors will become apparent in the investigation.”

The ship’s grounding is holding up $9.6bn worth of cargo each day between Asia and Europe, according to Lloyd’s List data.

Rabie estimated that Egypt is losing $12m-$14m in revenue from the canal for each day it is closed.

The United States also said it was ready to send support, including a team of US Navy experts.

Rabie thanked the US for its support along with China and the United Arab Emirates.

It remained unclear how long the blockage would last. Even after reopening the canal that links factories in Asia to consumers in Europe, the waiting containers are likely to arrive at busy ports, forcing them to face additional delays before offloading.

Apparently anticipating long delays, the owner of the stuck vessel diverted a sister ship, the Ever Greet, on a course around Africa instead, according to satellite data.

Others are following suit. The liquid natural gas carrier Pan Americas changed course in the mid-Atlantic, and now is aiming south to go around the southern tip of Africa, according to satellite data from MarineTraffic.com.