A "technical problem" could possibly have led to a Robben Island ferry partially sinking on Friday afternoon, the Robben Island Museum said.
The 64 passengers and four crew members aboad the ferry, Thandi, had to be evacuated when the nose of the boat started to sink in rough seas, 3km from the Cape Town waterfront.
Robben Island Museum senior ferry manager Sandresan Thandroyan said the ferry was used for the first time on Friday morning after undergoing lengthy maintenance work. He said the "technical problem" could have been made worse by severe weather conditions.
Thandroyan said an investigation however still needed to be completed to determine the cause of the vessel's problems. "From what we understand... there wasn't any damage to the boat itself," Thandroyan said.
The museum hires the vessel from Yacoob Yachts. Yacoob Yachts could not be reached for comment.
No passengers missing
Sea swells of up to 2m were reported in Cape Town on Friday afternoon, with winds of up to 65 km/h blowing from the south-southeast, South African Weather Service forecaster Stella Nake said.
Thandi departed from the Cape Town harbour at 10:42 and left the Island at 13:05.
The NSRI said it was activated at 14:18 to attend to passengers aboard the vessel.
Two NSRI vessels and a ferry from the Robben Island Museum ferried passengers and crew members to the waterfront, NSRI spokesperson Craig Lambinon said in a statement.
City of Cape Town fire and rescue services' Theo Layne said rescue operations were being complicated by extremely high seas and strong winds.
No one was reported missing.
Two women were taken to hospital for treatment - one complaining of back pain and another for mild hypothermia.
By Friday afternoon, authorities were still trying to retrieve Thandi from the ocean.
Safety measures were in place Thandroyan was unable to confirm whether the vessel sunk completely or not.
Asked why the vessel went out despite warnings of strong winds, Thandroyan said ferrying was declared safe by Thandi's master on Friday morning.
"We all are fully aware that in Cape Town the weather does turn quite quickly, especially with the South Easter, so we could not predict that it [would]," he said.
Thandroyan said all safety protocol was in place to save the lives of passengers. "Life jackets were in excess as required by legislation."
Robben Island Museum CEO Mava Dada apologised to passengers for the incident.
"The safety of our passengers is a key priority for us... As soon as we know what the cause was, we will share more information," he said in a statement.