Activists from the 'Free Gaza' group have defied Israel's siege of the territory, arriving at the port in Gaza City by boat from Cyprus, reported Aljazeera.
Dignity, a 20-metre chartered cruise boat, reached the Gaza Strip on Wednesday carrying 27 activists from 13 countries and half a tonne of medical supplies.
"I'm really concerned with what I'm hearing about a humanitarian crisis in Gaza," Mairead Corrigan McGuire, a Northern Ireland peace activist and Nobel prize winner in 1976, said before leaving Larnaca.
"We have a responsibility in the West, especially when children are suffering. I believe we can make a difference and break the silence of the international community."
Gaza's 1.5 million Palestinians have been suffering the effects of a crippling Israeli blockade since the Hamas movement took full control of the territory after pushing out security forces loyal to Mahmoud Abbas, the Palestinian president, in June 2007.
Since then there have been shortages of basic necessities such as food, fuel and medicines as Israel has strictly controlled all deliveries.
Last week, the International Committee of the Red Cross said that virtually no medical supplies were reaching the Gaza Strip, putting the lives of several hundred patients at risk.
"We got a list of zero stock medicines in Gaza, like baby formula, paracetamol, anti-histamine tablets," Ibrahim Hamami, a Palestinian-Briton and family physician from Buckinghamshire, said.
"There are basic things we can get over the counter in Europe but they do not have a single pill."
The trip was the second by the US-based group after two smaller fishing boats made the journey in August.
Organisers have said that they hope to make the trips into a monthly exercise in order to provide regular relief to the Gazans.
"We would like to do this once a month, but you need money to start a ferry service to Gaza," Derek Graham, the protest organiser, said.
Yigal Palmor, Israeli foreign ministry spokesman, had said the vessel would not be allowed to land in Gaza after activists in the previous group "took part in demonstrations and propaganda events organised by Hamas".
But Israeli navy vessels did not interfere as Dignity arrived in pouring rain on Wednesday.
Israel pulled its troops and settlers from Gaza in 2005 but still patrols the waters off the territory.