FRANKFURT (Reuters) - German carmaker Volkswagen said only half of its VW branded passenger car models in Germany are compliant with a new pollution standard, thanks to a much tougher emissions testing regime.

A Volkswagen logo is pictured at the International Auto Show in Mexico City, Mexico November 23, 2017. REUTERS/Henry Romero

Cars in the European Union must comply with the new Worldwide Harmonised Light Vehicle Test Procedure (WLTP) from September, but Volkswagen has only gained regulatory clearance for seven of its 14 main model lines.

“The new tests are more cumbersome and take two to three times longer than in the past, even limited edition models need to be tested separately,” Volkswagen’s Thomas Zahn said in a call with journalists on Thursday.

“The coming months will be challenging for us,” said Zahn, head of sales and marketing for Volkswagen passenger cars.

Volkswagen’s top-selling Golf model is among the vehicles still waiting to be cleared by authorities, Zahn said.

He said he expected the Golf to pass the WLTP standards by the end of September.

Shipments of cars are expected to slow down in September and October, but pick up again in the final two months of the year.

“We expect very strong deliveries in December,” Zahn said.

Carmakers including Daimler, Volkswagen and supplier Valeo have cut profit expectations, blaming a slowdown in global sales triggered in part by delays getting vehicles certified to the new standard.

Analysts at Evercore ISI said the WLTP delays at the VW brand appear to be under control since the carmaker has not resorted to heavy discounting to keep sales flowing.

Nonetheless delays will cause profitability of the brand to drop to around 2 percent in the third quarter, from 5.5 percent in the second quarter, Evercore said in a note on Thursday.