Many key component manufacturers in Japan are based in the worst-hit northeast regions, where facilities were damaged by the 9.0-magnitude earthquake on March 11 or inundated by the giant wave that followed.
Toyota has announced production disruptions domestically and in the United States, European Union, China and Australia because of the crisis, temporarily shutting some plants or running them at half-capacity or less.
On Friday it said it would also cut output in Thailand.
It said in a statement that "in Japan, depending on vehicle model, normalisation of production is expected to start in July, with normalisation completing around November or December."
Outside Japan, "normalisation" would start in August, the world's biggest auto maker said, and would also take until "around November or December" to be completed.
"To all the customers who made the decision to buy a vehicle made by us, I sincerely apologise for the enormous delay in delivery," said Toyota president Akio Toyoda at a news conference in Tokyo.
Asked about the likely effect on the auto giant's bottom line, Toyoda said only: "We have yet to comment on the impact on our profits. We want to tell you that at an appropriate time."
Toyota ended General Motors' 77-year reign as the world's largest automaker in 2008, but since then the Japanese giant has faced the impact of the global economic crisis, a massive safety recall crisis and a strong yen.
The company chief spoke about the impact of Japan's worst post-war disaster on the firm and the parts makers in its supply chain.
"Immediately after the earthquake, Toyota, like others, sent its employees into the disaster zone to join forces with our plants, dealers and suppliers to take steps toward recovery," he said.
"I too visited the affected areas several times. I saw people?s efforts first hand, and I was filled with confidence that their hard work would make possible a quicker recovery of production."
He pledged: "Our entire company is committed to solving the problems before us, so that we can achieve production recovery even one day sooner."
Toyota's Japan plants are now working at 50 percent of capacity and those in North America at 30 percent because of parts supply shortages.
The company said it plans to continue procuring parts from the same suppliers, but will also consider substitute parts from other firms.
The auto maker said about 150 parts were now affecting new-vehicle production -- mainly electronic, rubber and paint-related. However, replacement parts for sales, service and repair are available, it said.
|Visitors are seen inspecting a Toyota Passo at the company's showroom next to the headquarters in Toyota city, Aichi prefecture|
Shinichi Sasaki, Toyota executive vice president, said the company wanted to minimise the risk of bottlenecks in future.
"All the (production) lines can stop if something happens in just one place. We want to avoid that situation," he said.
"I would like our parts partners to do business close to our assembly lines. We also want to consider designs that aim to standardise parts so that we can have replacements."
Asked if Toyota wanted to speed up overseas procurement for production outside Japan, Sasaki said: "We want to raise the local procurement rate."
Sasaki also said there had been no impact on its vehicles from Japan's radiation-leaking Fukushima Daiichi nuclear power plant.
"In some countries, our customers ask whether Toyota cars are OK. But we are measuring radiation levels inside ships to each country," he said.
"If we monitor radiation twice as high as normal, we will stop it. But we have not heard about any such cases."