Najib also said a reconnaissance team would arrive in Dhaka on Monday consisting of diplomats and military officers to identify further assistance needed by the Rohingya.
Malaysia's armed forces chief said on Saturday that Kuala Lumpur would provide a 200-bed military field hospital in Bangladesh if the government there granted permission.
Describing Myanmar's inaction to halt the violence against innocent civilians as "rather disappointing", Najib said he will raise the Rohingya humanitarian tragedy with President Donald Trump on Sep 12 during his official visit to the White House.
"We have to help because the Rohingya tragedy has reached terrible proportions," he said.
On Friday, the powerful youth wing of Najib's dominant Malaysia's ruling party led a noisy street protest urging Kuala Lumpur to sever diplomatic ties with Yangon.
Malaysia on Tuesday summoned the Myanmar ambassador to voice its "deep concern" over the situation in Rakhine state, where witnesses said entire villages have been burned.
Over 1,000 people - more than twice the government's total estimate - may already have been killed in Rakhine, mostly Rohingya, said Yanghee Lee, the UN special rapporteur on human rights in Myanmar.
As of June this year, there are 59,100 Rohingya refugees registered with the UN Refugee Agency in Malaysia.